diphenyloxazole biosynthetic pathway in streptomyces ...

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IDENTIFICATION AND PRELIMINARY CHARACTERIZATION OF THE 2,5-

DIPHENYLOXAZOLE BIOSYNTHETIC PATHWAY IN STREPTOMYCES POLYANTIBIOTICUS SPRT.

by

Ian Kyle Kemp

A THESIS PRESENTED FOR THE DEGREE OF DOCTOR OF

PHILOSOPHY IN THE DEPARTMENT OF MOLECULAR AND CELL

BIOLOGY

FACULTY OF SCIENCE

UNIVERSITY OF CAPE TOWN

JULY 2015

The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non-commercial research purposes only.

Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author.

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TABLE OF CONTENTS

Acknowledgements .................................................................... ii

Abstract ..................................................................................... iii

Abbreviations ............................................................................ vi

CHAPTER 1 General introduction .................................................................. 1

CHAPTER 2 Early attempts at isolating the gene cluster responsible for DPO

biosynthesis in Streptomyces polyantibioticus SPRT ............... 59

CHAPTER 3 Streptomyces polyantibioticus SPRT genome exploration...... 101

CHAPTER 4 Development of a transformation protocol for Streptomyces

polyantibioticus SPRT and gene disruption experiments ....... 151

CHAPTER 5 General discussion ................................................................. 217

APPENDIX A ............................................................................................... 247

APPENDIX B ............................................................................................... 248

APPENDIX C ............................................................................................... 256

ii

ACKNOWLEDGEMENTS

The following people and organisations are thanked:

My supervisor, Dr Paul Meyers, for his assistance and support throughout the

duration of this project.

All the members of Lab 202/3 for their continuous support and advice, with

special mention to Gareth Everest and Sarah Curtis. It has been a pleasure

working with all of you.

The financial assistance of the National Research Foundation (NRF) towards

this research is hereby acknowledged. Opinions expressed and conclusions

arrived at, are those of the author and are not necessarily to be attributed to the

NRF.

The Medical Research Council and the University of Cape Town for the

financial support that made this project possible.

Dr P. Whitney Swain III for providing the plasmid vector pJN100 and E. coli

ET12567/pUZ8002 that were used in this study.

Dr Bohdan Ostash for providing the plasmid vector pOJ260 that was used in

this study and for the advice on Streptomyces transformation.

My parents, Ian and Anne-Marie, for their love, financial support and guidance,

especially during tough times.

To all academic staff, scientific officers and departmental assistants for all their

help and assistance.

iii

IDENTIFICATION AND PRELIMINARY CHARACTERIZATION OF THE 2,5-

DIPHENYLOXAZOLE BIOSYNTHETIC PATHWAY IN STREPTOMYCES POLYANTIBIOTICUS SPRT.

by

Ian Kyle Kemp

Department of Molecular and Cell Biology, University of Cape Town, Private

Bag, Rondebosch, 7701, South Africa

ABSTRACT

An antibacterial compound produced by the actinomycete, Streptomyces

polyantibioticus SPRT, exhibited antibiosis against Mycobacterium tuberculosis

H37RvT (the causative agent of tuberculosis), which prompted interest in its

biosynthesis. The antibacterial compound was isolated in a previous study and its

structure was determined by X-ray crystallography and nuclear magnetic resonance

(NMR) to be 2,5-diphenyloxazole (DPO). Based on the structure of DPO, a biosynthetic

scheme for the synthesis of this molecule was proposed, whereby a non-ribosomal

peptide synthetase (NRPS) condenses a molecule of benzoic acid with 3-

hydroxyphenylalanine. The dipeptide is converted to a diphenyloxazole derivative by

heterocyclization and a final decarboxylation step leads to DPO. To determine whether

the hypothesis pertaining to the DPO biosynthetic pathway was correct, initial efforts

were made to identify the genes coding for benzoic acid synthesis and the DPO NRPS

in the S. polyantibioticus SPRT genome using PCR amplification, Southern

hybridization and sequencing. This led to the identification of 12 unique adenylation

(A) domains (of which one was specific for phenylalanine) and a gene, paaK, encoding

a phenylacetate CoA-ligase (PA-CoA), putatively involved in benzoic acid

biosynthesis. However, no further sequence information could be obtained for the

genes encoding the phenylalanine-specific A domain or PA-CoA and similar attempts

to identify other NRPS-associated domains, as well as genes involved in benzoic acid

synthesis, proved unsuccessful. In light of these difficulties, the S. polyantibioticus

iv

SPRT genome was sequenced and a gene cluster was identified as being responsible for

the biosynthesis of DPO using a genome mining approach. However, contrary to the

hypothesis that a linear NRPS system for DPO biosynthesis would be identified, the

gene cluster exhibited a nonlinear arrangement. The core domains are arranged as A-

PCP-C (instead of C-A-PCP) and there is also a stand-alone heterocyclization (Cy)

domain, a stand-alone thioesterase (TE) domain and an acyl-CoA synthetase putatively

involved in activating benzoic acid. Furthermore, there are two NRPS domains in the

gene cluster that are believed to be inactive. A possible biosynthetic pathway for

benzoyl-CoA production, encoded by a separate gene cluster, was identified based on

the genome analysis of S. polyantibioticus SPRT. In order to confirm the involvement

of the identified genes in DPO biosynthesis, an intergeneric conjugation protocol was

developed for the introduction of plasmid DNA into S. polyantibioticus SPRT and

subsequent gene disruption experiments. The putative DPO biosynthetic genes were

insertionally activated via homologous recombination and the method for isolating

DPO was carried out on each of the mutant strains, after which the extracts were assayed

for activity against Mycobacterium aurum A+ using TLC-bioautography analysis. The

absence of activity against M. aurum A+ in the extracts from mutant strains S.

polyantibioticus ∆A99, S. polyantibioticus ∆CYC and S. polyantibioticus ∆ACY

suggested the involvement of the A domain encoded by gene SPR_53060, the putative

Cy domain encoded by gene SPR_53040 and the acyl-CoA synthetase encoded by gene

SPR_52860 in the biosynthesis of DPO. However, attempts to identify the genes

responsible for benzoic acid biosynthesis proved unsuccessful, as gene disruption did

not abolish DPO activity in the S. polyantibioticus ∆LAC, S. polyantibioticus ∆PAAK

and S. polyantibioticus ∆CIN mutant strains encoding the putative D-lactate

dehydrogenase encoded by gene SPR_60250, the PA-CoA ligase (paaK) encoded by

gene SPR_46390 and the cinnamate-CoA ligase encoded by gene SPR_60150,

respectively. Based on the genome annotation analysis and gene disruption studies, a

model for DPO biosynthesis is proposed. At this stage, the model cannot account for

the source of benzoic acid, as in vivo gene disruption experiments disproved both of the

hypotheses on how benzoic acid is synthesized in S. polyantibioticus SPRT. However,

alternative hypotheses regarding the mechanism of benzoic acid biosynthesis in S.

polyantibioticus SPRT are proposed and are suggested as the place to start in future

studies to elucidate the production of this unusual starter unit in DPO biosynthesis.

Furthermore, the identification of the gene cluster responsible for DPO biosynthesis has

v

laid the foundation for future combinatorial biosynthetic studies to create derivatives of

DPO that might be used in the treatment of drug resistant tuberculosis. Lastly, the S.

polyantibioticus SPRT genome sequence could be explored for the identification of

antibiotic gene clusters for other potential antitubercular antibiotics that this organism

produces.

vi

ABBREVIATIONS

α alpha β beta ∆ delta γ gamma λ lambda Ω ohm (s) Φ phi µg microgram(s) µl microlitre(s) µF microFarad (s) µM micromolar °C degrees Celsius % percentage A adenylation domain aprR apramycin resistant AIDS Acquired Immunodeficiency Syndrome ACP acyl carrier protein ArCP aryl carrier protein ATP adenosine triphosphate AMP adenosine monophosphate AMT aminotransferase BC Before Christ bp base pair(s) BLAST Basic Local Alignment Search Tool C condensation domain Cy heterocyclization domain CDC Centers for Disease Control and Prevention CDD Conserved Domain Database clt cis-acting locus of transfer COGs clusters of orthologous groups COM communication-mediating CoA Coenzyme A DMSO dimethyl sulphoxide DNA deoxyribonucleic acid dsDNA double-stranded DNA ssDNA single-stranded DNA

vii

dH20 distilled water DPO 2,5-diphenyloxazole dNTP deoxyribonucleoside triphosphates (dATP, dCTP, dTTP and dGTP) et al. and others (et alii) E epimerization domain FAS fatty acid synthase FMN flavin mononucleotide g gram(s) gDNA genomic DNA GrsA gramicidin synthetase HAL histidine ammonia-lyase HIV Human immunodeficiency virus HM Hacène’s medium HMM Hidden Markov Model HPLC High-performance liquid chromatography h hour(s) Inc. Incorporated IncP Incompatibility group P ISP International Streptomyces Project IPTG isopropyl-β-D-thiogalactopyranoside kb kilobase(s) kg kilogram(s) kDa kiloDalton(s) kV kiloVolt(s) l litre LA Luria-Bertani agar LB Luria-Bertani broth M molar MDR multidrug-resistant MEGA Molecular Evolutionary Genetics Analysis ML maximum likelihood MP maximum parsimony MRSA methicillin-resistant Staphylococcus aureus MS mannitol soya MT methyltransferase Mb mega base(s)

viii

mg milligram(s) min minute(s) ml millilitre(s) mM millimolar mm millimetre(s) mRNA messenger RNA ms millisecond (s) mA milliAmp(s) NADP Nicotinamide adenine dinucleotide phosphate NGS Next-generation sequencing NJ neighbour joining NRPS Non-ribosomal peptide synthetase NRP Non-ribosomally synthesized peptide ng nanogram(s) nm nanometre(s) OD optical density ORF open reading frame oriT origin of transfer Ox oxidation domain O/N overnight PA phenylacetate PA-CoA phenylacetate-CoA ligase PAL phenylalanine ammonia-lyase PCP peptidyl carrier protein PCR polymerase chain reaction PDR pan drug-resistant PEG polyethylene glycol PKS Polyketide Synthase PPi inorganic pyrophosphate PPTase phosphopantetheinyltransferase PP phosphopantetheine p plasmid RAST Rapid Annotation using Subsystem Technology RE reduction domain Rf retention factor REase restriction endonuclease RSA Republic of South Africa R-M restriction-modification RNA ribonucleic acid RNase ribonuclease

ix

rpm revolutions per minute s second(s) SEM standard error of the mean SAM S-adenosylmethionine SDS sodium dodecyl sulphate SSC standard saline citrate spp. species (plural) T type strain TB Tuberculosis TE thioesterase domain TLC thin layer chromatography TSB tryptic soy broth TSVM transductive support vector machine U unit(s) USA United States of America UK United Kingdom UV ultraviolet VRSA vancomycin-resistant Staphylococcus aureus v/v volume per volume V volt(s) WHO World Health Organisation XDR extensively drug-resistant YEME yeast extract-malt extract medium (ISP Medium No.2) ZMW zero-mode waveguide

x

1

CHAPTER 1

GENERAL INTRODUCTION

2

CHAPTER 1


1.1 Antibiotic resistance........................................................................................... 3

1.2 The phylum Actinobacteria ............................................................................... 9

1.3 Natural product discovery ................................................................................ 11

1.3.1 Oxazole-containing natural prdoucts ................................................... 14

1.4 Non-ribosomal peptide synthetases (NRPSs) .................................................. 17

1.4.1 Assembly logic of NRP synthesis ........................................................ 20

1.4.1.1 Activation by the Adenylation domain .................................... 21

1.4.1.2 Transport of substrates and intermediates to the catalytic

centres by the Peptidyl Carrier Protein .................................... 23

1.4.1.3 Peptide elongation by the Condensation domain ..................... 24

1.4.1.3.1 Heterocyclization domains............................... 27

1.4.1.4 Peptide release by the Thioesterase domain ............................ 29

1.4.1.5 Editing/tailoring domains......................................................... 31

1.4.1.5.1 Methylation ...................................................... 31

1.4.1.5.2 Epimerization (control of stereochemistry) ..... 32

1.4.1.5.3 Reduction domain ............................................ 32

1.4.1.5.4 Oxidation domain............................................. 33

1.4.1.5.5 Further modifications ....................................... 34

1.4.2 NRPS substrate specificity prediction and the non-ribosomal code .... 35

1.4.3 NRPS biosynthetic strategies ............................................................... 41

1.4.4 Combinatorial biosynthesis and intermolecular communication ......... 45

1.5 Research aims .................................................................................................. 47

1.6 Reference list ................................................................................................... 50

Chapter 1 - Introduction

3

CHAPTER 1


The existence of antimicrobial agents was first described in 1877 when Louis Pasteur

and Robert Koch observed that one type of bacterium could prevent the growth of

another. The term “antibiosis’ was introduced by the French bacteriologist, Vuillemin,

as a descriptive name for this phenomenon. In 1942, Selman Waksman, an American

microbiologist, devised the term antibiotic to describe any substance produced by a

microorganism that is antagonistic to the growth of other microorganisms in high

dilution (Waksman, 1947). The value of antibiotics to medicine was soon realized and

it lead to the heightened interest in the isolation and discovery of these novel

compounds. Indeed, the rapid development of antimicrobial agents over the past

century has greatly improved the treatment of infection and disease. However, the

increased usage of these drugs in the 1950s sparked the arms race between humanity

and microbial pathogens, as increased examples of recalcitrant infections due to the

inevitable rise of drug-resistant pathogens became apparent (Davies, 2012; Davies,

2007).

1.1 ANTIBIOTIC RESISTANCE

The use of antibiotics as a means of treating infectious disease in humans and food-

producing animals has revolutionized medicine and become widespread since the

introduction of penicillin in the 1940s. Regrettably, the extensive misuse of these drugs

in both the clinical and agricultural setting has led to the rapid emergence of drug-

resistant strains of bacteria and other microbes. This resistance has led to a decrease in

the effectiveness of currently available antimicrobial drugs and the problem is further

compounded by the emergence of multidrug-resistant microbial strains.


4

Microorganisms that have developed resistance to several different antibiotics are

referred to as multidrug-resistant (MDR) strains.

It was reported in 2004 that more than 70 % of pathogenic bacteria were predicted to

be resistant to at least one of the currently available antibiotics. Although we have

witnessed a steady increase in resistance in almost every pathogen to most of the

currently available antibiotics, not all of these antibacterial agents display the same rate

of resistance development. Indeed, single target drugs such as rifampicin are more

susceptible to the development of resistance than drugs that inactivate several targets

irreversibly, such as penicillin (Demain & Sanchez, 2009; Spratt, 1994).

Global healthcare systems are also encountering extensively drug-resistant (XDR)

organisms on a regular basis and these microorganisms are resistant to all antibiotics

except colistin, a highly toxic agent, which was abandoned in the 1960s due to its

questionable efficacy. In the most severe case, certain microorganisms are pan drug-

resistant (PDR), meaning that they are resistant to all available antibiotics (Udwadia &

Vendoti, 2013; Udwadia, 2012).

It has been reported that at least 2 million people become infected with antibiotic-

resistant bacteria each year in the United States, with at least 23 000 people dying as a

direct result of these infections. It is also believed that most deaths related to antibiotic

resistance happen in healthcare facilities such as nursing homes and hospitals. One of

the most common causes of healthcare-associated infections is methicillin-resistant

Staphylococcus aureus (MRSA), claiming the lives of more than 11 000 people in the

United States in 2011. This MDR, Gram-positive pathogen is resistant to all penicillins

and cephalosporins (i.e. all β-lactam antibiotics), as well as often being resistant to

clindamycin and quinolones. S. aureus bacteria produce a biofilm which protects them

from the environment. These biofilms can grow on wounds, scar tissue and medical

implants or devices (Dantas & Sommer, 2014). It is estimated that more than 70 % of

the bacterial species that produce biofilms are likely to be resistant to at least one of the

drugs commonly used in anti-infectious therapy in hospitals (Demain & Sanchez,

2009). Once described as only a hospital-inhabiting or nosocomial infection, the rate

of MRSA infections has increased rapidly among the general population in the past


5

decade, which further exacerbates the urgent need for new therapeutic agents (Centers

for Disease Control and Prevention, 2013).

Vancomycin has long been the treatment of choice for MRSA infections, however, new

treatments were sought after the Centers for Disease Control and Prevention (CDC)

reported the first case of S. aureus resistant to both methicillin and vancomycin in 2002.

Since then, the number of reported cases of vancomycin-resistant S. aureus (VRSA)

has remained relatively low and thus the epidemiology and risk factors associated with

VRSA are not completely understood. Further research is required in order to

understand these aspects, as well as the implications pertaining to clinical and infection

control and optimal treatment (Howden et al., 2010; Applebaum, 2006).

Pathogens that are less prevalent than MRSA, but that pose a threat of infection that is

genuinely untreatable are those such as the carbapenem-resistant Enterobacteriaceae.

Within this large family of Gram-negative bacteria, strains of Acinetobacter baumannii,

Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa are currently

tormenting global healthcare systems due to their resistance to all β-lactam antibiotics.

This resistance is conferred by the ability of their outer membrane to prevent the entry

of the antibiotics, in addition to being able to expel, via efflux pumps, the remainder

that does successfully enter the cell (Fischbach & Walsh, 2009).

Furthermore, a report released by the CDC in 2013 identified the pathogens Clostridium

difficile and Neisseria gonorrhoeae as antibiotic-resistant bacteria that require urgent

public health attention in order to identify infections and limit transmission (CDC,

2013). The report also highlighted the serious threat of MDR and XDR strains of

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB).

Tuberculosis is a contagious airborne disease and is second only to human

immunodeficiency virus (HIV)/AIDS as the leading killer worldwide due to a single

infectious agent (Liu et al., 2012). Approximately 9 million people contracted TB in

2013, of which 1.5 million people died from the disease. About 480 000 people

developed MDR-TB globally in 2013, an increase of almost 7 % from 2012, of which

more than half the cases were in developing countries such as India, China and the


6

Russian Federation. It was also estimated that 9 % of the MDR-TB cases had XDR-

TB (World Health Organisation, 2014)

In the majority of cases, TB is treatable and curable with the available first-line anti-

TB drugs (rifampicin, isoniazid and pyrazinamide). However, disease caused by M.

tuberculosis strains that are resistant to one or more of these standard drugs is far more

challenging to treat, largely due to the higher cost, adverse side-effects and longer

treatment regimes of the available second-line drugs. MDR-TB strains are defined as

being resistant to at least two of the first-line anti-tubercular drugs, isoniazid and

rifampicin. XDR-TB strains are defined as being resistant to both these drugs as well

as to any fluoroquinolone and at least one of the injectable second-line drugs (i.e.

kanamycin, amikacin or capreomycin). Extensively drug-resistant TB has been

identified in 92 countries and in all regions of the world (WHO, 2014; CDC, 2013;

Rivers & Mancera, 2008; Petrini & Hoffner, 1999).

The primary cause of MDR-TB and XDR-TB is incomplete or incorrect treatment,

which is mainly attributed to patients not completing their full course of antibiotic

therapy, but is also due to the usage of inappropriate drug combinations, poor treatment

compliance, using single drugs for ordinary TB, clinics running out of drug stocks and

the use of poor quality medicines (WHO, 2014; Cape Gateway, 2006).

The World Health Organisation (WHO) has predicted that between 2000 and 2020,

almost 1 billion people globally will contract tuberculosis and that the disease will claim

the lives of approximately 35 million people. Twenty-two high-burden countries were

identified, which account for 81 % of all estimated TB cases that occur globally. South

Africa has the highest incidence of TB in the world per capita population and this

problem is compounded by the high incidence of HIV co-infection, as HIV-positive

individuals infected with M. tuberculosis have a dramatically increased chance of

developing TB compared to TB-infected, HIV-negative individuals (Churchyard et al.,

2014; Bloom and Murray, 1992). South Africa also has the largest number of HIV-

associated TB cases and the second-largest number of MDR-TB cases, after India.

Notable progress has been achieved in reducing TB prevalence and deaths and

improving treatment outcomes for new TB cases in recent years, but the burden still

remains enormous, especially considering the drastic rise in the numbers of MDR and


7

XDR strains. New TB drugs and vaccines are urgently required to further accelerate

progress towards improved TB control in South Africa and other countries (Churchyard

et al., 2014).

Consequently, there is a global healthcare emergency, as new antibiotic discovery and

subsequent treatment options have been outpaced by the emergence of drug-resistant

microorganisms. In order to control the global TB epidemic, there is an urgent need

for new and improved TB drugs. These new drugs should, ideally, be effective against

both MDR and XDR M. tuberculosis strains, be able to shorten the duration of treatment

from the current six month regime and simplify treatment by reducing the number of

pills that need to be taken each day, as well as reducing the dosage frequency to once a

week. In addition, new TB drugs should be able to be administered simultaneously

with HIV drugs and be effective against latent TB (Koul et al., 2011; Lamichhane,

2011; Barry et al., 2009; Young et al., 2009; Rivers and Mancera, 2008).

In light of this, taxonomy-guided bacterial bioprospecting needs to continue to play an

important role in identifying new microbial natural products, such as bacterial

secondary metabolites that have already served the pharmaceutical industry well as TB

drugs. It has been estimated that less than 10 % of the world’s biodiversity has been

tested for biological activity, so there is a high likelihood of isolating new antibiotic

molecules from bacteria (Ashforth et al., 2010; Harvey, 2000).

In addition, the relentless evolution of antibiotic-resistant strains of microbial

pathogens erodes the utility of the classical antibiotics and necessitates the perpetual

need for discovery of new antibiotics (Ashforth et al., 2010). Consequently, numerous

research groups are now focussing on identifying novel antibiotics in new species of

Streptomyces and other genera of Actinobacteria due to the fact that they are renowned

for their ability to produce antibiotics and other bioactive natural products with a wide

range of applications in medicine and agriculture. Examples of these compounds

include antibacterials such as erythromycin A, vancomycin and daptomycin,

antifungals such as amphotericin B, immunosuppressants such as FK-506, anticancer

agents such as doxorubicin and epoxomicin, anthelmintics such as avermectin,

insecticides such as spinosyn A and herbicides such as phosphinothricin (Figure 1.1)

(Challis, 2014).


8

Figure 1.1 Examples of secondary metabolites used in medicine and agriculture produced by

Actinobacteria (Challis, 2014).


9

1.2 THE PHYLUM ACTINOBACTERIA

The phylum Actinobacteria represents one of the largest taxonomic units within the

domain Bacteria and is predicted to be the most abundant source of small molecule

diversity on earth (Miao & Davies, 2010). The phylum consists of Gram-positive

bacteria with typically elevated guanosine (G) and cytosine (C) content in their

chromosomal DNA, ranging from 50 % in certain corynebacteria to more than 70 % in

Streptomyces and Frankia species (Ventura et al., 2007).

Actinobacteria are inhabitants of soil, the rhizosphere, marine and extreme arid

environments and exhibit a wide range of morphologies, including coccoid, rod-shaped

and hyphal forms. The filamentous actinobacteria are often referred to as

actinomycetes and produce branching hyphae which form a mycelium. In many genera

of actinomycetes, some of the vegetative hyphae differentiate into arthrospores. Some

genera of actinomycetes exhibit fragmentation in liquid and/or plate culture (e.g.

Amycolatopsis), a phenomenon in which the vegetative hyphae break down into rod-

shaped or coccoid elements. Additionally, actinobacteria are able to produce a variety

of extracellular enzymes and secondary metabolites as a result of the regulated

expression of gene clusters (MacNeil et al., 1992; Chater, 1990). Interest in the phylum

intensified after the discovery of streptomycin in the laboratory of Selman Waksman in

1943 and the subsequent observation that many of the secondary metabolites are indeed

potent antibiotics. In particular, Streptomyces species have been exploited extensively

by the pharmaceutical industry as a primary source of natural products for use as

therapeutic agents, but bacteria belonging to the suborders Micromonosporineae (e.g.

Micromonospora), Pseudonocardineae (e.g. Amycolatopsis) and Streptosporangineae

(e.g. Planobispora) have also been described as abundant producers of novel

antibacterial antibiotics (Ashforth et al., 2010; Miao & Davies, 2010; Ventura et al.,

2007).

Actinobacterial genomes, particularly those of the actinomycetes (order

Actinomycetales), are larger than most other bacteria, with sizes ranging from 0.93 Mb

(Tropheryma whipplei) to 11.9 Mb (‘Streptomyces bingchenggensis’) and therefore

possess a high capacity for secondary metabolite production (Verma et al., 2013).


10

Among the actinomycetes, such as Streptomyces, it is estimated that more than 60 % of

the secondary metabolites produced are synthesized by enzymatic systems known as

non-ribosomal peptide synthetases (NRPSs), polyketide synthases (PKSs) or mixed

NRPS-PKS pathways (Baltz, 2014). Moreover, it is widely accepted that species that

possess a large number of NRPS and/or PKS genes produce more secondary

metabolites. For example, the sequencing of the first antibiotic-producing

actinomycete genomes, those of Streptomyces coelicolor strain A3(2) (8.6 Mb) and

Streptomyces avermitilis strain MA-4680T (9.02 Mb), revealed the potential of both

organisms to produce a large number of secondary metabolites, most of which were not

synthesized under standard growth conditions (Baltz, 2008).

The genome sequence of S. avermitilis MA-4680T revealed 24 PKS and NRPS clusters

for previously unidentified secondary metabolites and in the case of S. coelicolor A3(2),

a genome mining approach identified the capability of the organism to produce twice

as many secondary metabolites as was originally thought (Nett et al., 2009; Bentley et

al., 2002). Similarly, annotation of the genomes of S. avermitilis MA-4680T and

Streptomyces griseus strain NBRC 13350, revealed that 60 % and 75 %, respectively,

of the biosynthetic gene clusters in these organisms encoded unidentified secondary

metabolites, further suggesting that natural product biosynthetic capacity has been

immensely underestimated (Challis, 2014; Nett et al., 2009; Walsh, 2004; Challis &

Ravel, 2000).

The sequenced actinobacterial genomes (currently numbering 4059) (GenBank, 2015;

Land et al., 2015) are an invaluable resource which has revealed that the more bacterial

genomes that are sequenced, the more new gene families are discovered, thus

uncovering new genetic diversity and thereby new biosynthetic capabilities (Wu et al.,

2009). This genetic diversity is directly afforded by NRPS multifunctional enzymatic

systems that are able to manufacture structurally diverse natural products with a

remarkable variety of useful/significant pharmacological activities (Ashforth et al.,

2010; Wu et al., 2009).


11

1.3 NATURAL PRODUCT DISCOVERY

Natural products, which can be produced from primary or secondary metabolism by

living organisms such as bacteria, plants, mammals, marine invertebrates, insects and

fungi, are defined as low molecular weight, organic molecules (Davies & Ryan, 2012).

The bacterial metagenome contributes to the production of primary metabolites and

conversion of small molecules into secondary metabolites, also called “specialized

metabolites”. Two of the important classes of secondary metabolites classified as

natural products are the polyketides and non-ribosomal peptides. Other structural

classes include alkaloids, terpenoids, aminoglycosides and shikimate-derived

molecules (Baltz, 2014; Davies & Ryan, 2012).

For over half a century, natural products have played an important role as targets of

study for analytical and synthetic chemists, as chemical tools for probing biological

systems to aid in discovering the roles of individual biomolecules, but most

importantly, they have acted as a treasure trove of compounds used to treat infectious

diseases in humans, animals and crops (Davies, 2011; Fischbach & Walsh, 2009).

Indeed, it has been estimated that approximately 40 % of all medicines in clinical use

are either natural products or their semi-synthetic derivatives (John, 2009). This may

not come as a surprise, considering that herbal medicine formed the cornerstone of

sophisticated traditional medicine practices, with the earliest records dating back to

2600 BC in Mesopotamia, where plant-derived substances such as the oils of Cupressus

semevirens (cypress), Cedrus species (cedar) and Glycyrrhiza glabra (licorice) where

used to treat ailments such as coughing, parasitic infections and inflammation (Cragg

& Newman, 2013; John, 2009). It has also been documented that the Greeks and

Romans contributed significantly to the development of the use of herbal medicine in

the ancient Western world (Cragg & Newman, 2013).

Furthermore, the serendipitous discovery of morphine in 1805 was the first

pharmacologically active pure compound isolated from a plant. This organic alkaloid

was derived from the resinous gum secreted by Papaver somniferum (the opium poppy)

and sparked the study of alkaloid chemistry, which inadvertently accelerated the

emergence of the modern pharmaceutical industry. Similar alkaloids from organic


12

substances were isolated soon after, such as strychnine in 1817, caffeine in 1820 and

nicotine in 1828 (Li & Vederas, 2009).

In contrast, the microbial-derived drug era began in the 1920s with the discovery of the

antibiotic, penicillin, by Sir Alexander Fleming. Penicillin was later produced

industrially as a powder and used as a potent antibacterial compound during World War

II. The observation of its broad therapeutic use started what became known as “The

Golden Age of Antibiotics” and prompted the massive screening of microorganisms for

new antibiotics and related novel bioactive molecules (Cragg & Newman, 2013).

By 1990, 80 % of therapeutic medicines were natural products or analogues inspired by

them (Li & Vederas, 2009). Microorganisms remain a prolific source of structurally

and chemically diverse bioactive metabolites and these include antibacterial agents,

such as the penicillins (from Penicillium species), cephalosporins (from

Cephalosporium acremonium), aminoglycosides, tetracyclines and other polyketides of

many structural types (from members of the order Actinomycetales);

immunosuppressive agents, such as the cyclosporins (from Trichoderma and

Tolypocladium species) and rapamycin (from Streptomyces species); cholesterol-

lowering agents, such as mevastatin (compactin; from Penicillium species) and

lovastatin (from Aspergillus species); and anthelmintics and antiparasitic drugs, such

as the ivermectins (from Streptomyces species) (Cragg & Newman, 2013; Demain &

Sanchez, 2009; Li & Vederas, 2009).

Historically, the classical screening and bioassay-guided isolation techniques were very

successful in providing a route to the discovery of novel natural products for the

development of new therapeutic agents (Subramani & Aalbersberg, 2013). Over the

past two decades, however, natural product discovery efforts, particularly microbially-

produced products, have waned considerably due to the high rediscovery rate of known

compounds. Most of the common core structures from which today’s antibiotics are

derived were introduced between the mid-1930s and the early 1960s (Figure 1.2)

(Fischbach & Walsh, 2009). Consequently, pharmaceutical firms have preferred to

pursue alternative options in their search for new therapeutic agents, such as chemically

tailored derivatives of the classical scaffolds and modern techniques such as in silico


13

screening, combinatorial biosynthesis (Cane et al., 1998) and combinatorial

biocatalysis (Watve et al., 2001; Michels et al., 1998).

Figure 1.2 No new major classes of antibiotics were introduced between 1962 and 2000 (referred

to as an innovation gap) (Fischbach & Walsh, 2009).

Despite this lack of interest, natural products continue to provide greater structural

diversity than standard combinatorial chemistry and therefore offer far more

opportunities for finding novel chemical scaffolds that are active against a wide range

of targets. In addition, the majority of the world’s biodiversity remains unexplored and

it has become increasingly apparent that approximately only 1 % of the microbial

diversity has been cultured and studied experimentally (Van Lanen & Shen, 2006;

Harvey, 2000). Attempts at exploring the uncultured or allegedly unculturable bacteria

using culture-independent methods such as metagenomics have been investigated and

it has become evident that these bacteria may in fact be culturable, thus providing a

potentially large source of new bioactive compounds (Watve et al., 2001; Handelsman

et al., 1998; Hugenholtz et al., 1998; Seow et al., 1997).


14

Nevertheless, it was reported in 2005 that the number of discovered natural products

exceeds 1 million and this is mainly due to improvements in screening methods, as well

as separation and isolation techniques. Among these compounds, it is estimated that

50-60 % are produced by plants and 5 % are produced by microbes. Furthermore, it is

approximated that from the pool of biologically active compounds obtained from

microbes, 45 % are produced by actinomycetes, 38 % by fungi and 17 % by unicellular

bacteria (Bérdy, 2005).

There is still a gigantic proportion of undiscovered metabolites produced by the

actinomycetes and predictive modelling by Watve et al. (2001) suggested that more

than 150 000 bioactive metabolites are still waiting to be discovered from the members

of the genus Streptomyces alone. In order to gain access to the biodiversity afforded in

these and other actinobacterial suborders, it is imperative to continue efforts to isolate

novel actinobacteria from underexplored, diverse natural habitats.

There has been an increasing number of novel secondary metabolites isolated from

actinobacteria, specifically from the genus Streptomyces, over the past few decades,

and one such class is the heterocyclic-ring containing metabolites such as the oxazoles

and thiazoles. Several of these metabolites have been shown to exhibit extremely useful

biological properties, such as antimycobacterial activity (Walsh & Fischbach, 2010).

1.3.1 Oxazole-containing natural products

Oxazoles are aromatic 5-membered heterocycles which contain both nitrogen and

oxygen (Yeh, 2004). They are produced in nature by dramatic chemical modifications

performed on elongating peptide chains, most often catalysed by NRPS assembly lines

(Walsh et al., 2001). Oxazole biosynthesis is achieved via the cyclodehydration of

serine or threonine to yield a dihydroheteroaromatic oxazoline, which is then subjected

to a two-electron oxidation step and in turn yields the oxazole core structure (Figure

1.3). Reduction of the carbon-nitrogen bond in oxazoline creates an oxazolidine ring

(Yeh, 2004; Roy et al., 1999, Milne et al., 1998). All three of these oxidation states

can be found in natural products and if the starting residue is cysteine, the corresponding

process would yield thiazolines, thiazoles and thiazolidines (Roy et al., 1999; Milne et

al., 1998).


15

Figure 1.3 Schematic representation of the biosynthetic process involved in oxazole and thiazole

production (Roy et al., 1999).

It was initially considered that naturally occurring oxazoles were rare, until heightened

research in the 1980s proved their ubiquity in nature (Yeh, 2004). The anticonvulsant

alkaloid, pimprinine, was one of the earliest oxazole-containing compounds to be

discovered, which was isolated from ‘Streptomyces pimprina’ in 1960 (Bhate et al.,

1960). Two related alkaloids, pimprinethine and pimprinaphine, were isolated almost

twenty years later from Streptomyces cinnamoneus and Streptomyces olivoreticuli,

respectively (Yoshioka et al., 1981). Furthermore, in 1966, the macrocyclic

streptogramin antibiotic accommodating a 2,4-disubstituted oxazole ring,

virginiamycin M2, was isolated from Streptomyces virginiae (Kondo et al., 1989). The

2,4-disubstituted oxazole ring is a common feature in several cyclic peptide natural


16

products including the antileukemic metabolites, orbiculamide and keramide E, which

were both isolated from the marine sponge, Theonella sp., in 1991 (Fusetani et al.,

1991) and 1995 (Kobayashi et al., 1995), respectively. Additionally, in 1998, Rastogi

and colleagues reported the antimycobacterial activity of the oxazole alkaloid, texaline,

isolated from the plants Amyris texana and Amyris elemifera (Rastogi et al., 1998).

The stimulated interest in oxazoles (and thiazoles) can be attributed to their diverse

biological properties and their ability to interact with a wide variety of intracellular

bacterial targets, specifically proteins, DNA and RNA (Walsh, 2004; Milne et al.,

1998). Additionally, the oxazoline and thiazoline rings are important elements of

bioactive natural products and well known antimicrobial products. The use of these

rings as building blocks in pharmaceutical drug discovery is continually increasing and

one example is the phenyloxazolines which are able to inhibit the growth of certain

Gram-negative bacteria by impeding the production of lipid A, a molecule located in

the outer membrane of most Gram-negative bacteria (Padmavathi et al., 2009; Jackman

et al., 2000).

The biosynthesis of several oxazoles, thiazoles and their derivatives has been reported

to be catalysed by NRPS and NRPS/PKS hybrid enzyme complexes. Examples include

tallysomycin produced by Streptoalloteichus hindustanus ATCC 31158 (Tao et al.,

2007), virginiamycin produced by S. virginiae (Pulsawat et al., 2007) and zorbamycin

produced by Streptomyces flavoviridis ATCC 21892 (Wang et al., 2007). More

recently, novel antitrypanosomal antibiotics, the spoxazomicins, containing an oxazole

moiety within their structure, were isolated from the endophytic actinomycete,

Streptosporangium oxazolinicum. However, the biosynthetic machinery involved in

the synthesis of the spoxazomicins is yet to be elucidated (Inahashi et al., 2011).


17

1.4 NON-RIBOSOMAL PEPTIDE SYNTHETASES (NRPSs)

Non-ribosomally synthesized peptides (NRPs) represent a class of microbial natural products

that exhibit unparalleled diversity in both structure and biological activity. These

characteristics can be attributed to the incorporation of many unusual, nonproteinogenic

residues and modifications (Konz & Marahiel, 1999; Marahiel, 1997). As the name implies,

NRPs are normally synthesized from amino acids, but over 400 monomers are known to be

used as substrates, which include non-proteinogenic amino acids such as ornithine and

hydroxyphenylglycine, D-configured and N-methylated amino acids, as well as a variety of

hydroxyl-amino acids, which can be further modified by acylation, glycosylation and

heterocyclic ring formation mediated by associated tailoring enzymes (Bloudoff et al., 2013;

Konz & Marahiel, 1999). Despite the structural diversity, however, the majority of NRPs share

a common biosynthetic origin, which has been linked to an enzymatic system known as the

“thiotemplate multienzymic mechanism” (Marahiel, 1997; Kleinkauf & von Döhren, 1990).

This enzymatic system is more commonly referred to as a non-ribosomal peptide synthetase

(NRPS) and these large, multifunctional enzymes range in size from 100-2000 kDa and can

catalyze up to several dozen reactions in a co-ordinated, assembly-line manner (Mootz et al.,

2002; Cane & Walsh, 1999; Marahiel, 1997).

Non-ribosomal peptide biosynthesis is widespread in a variety of bacterial and fungal species

and plays a significant role in the production of several biologically relevant products

(Schwarzer et al., 2003). These include antibiotics such as bacitracin A, surfactin,

tyrocidine A, gramicidin S and the penicillin precursor, isopenicillin N; immunosuppressive

agents such as cyclosporin (used in the aftercare of organ transplant patients); bleomycin A2

and epothilone (used in cancer therapy due to their cytostatic activity); and siderophores such

as enterobactin and myxochelin A (Figure 1.4) (Schwarzer et al., 2003: Marahiel, 1997).

Additionally, the genes encoding bacterial NRPSs are organised into operons, which are

usually 6-45 kilobases in length and encode protein templates that are often much smaller than

their fungal counterparts (Marahiel, 1997).


18

Figure 1.4 The chemical structures of some bacterial (gramicidin S, bacitracin A, tyrocidine A, surfactin

and enterobactin) and fungal (cyclosporin A and isopenicillin) bioactive compounds whose

peptide backbones are synthesized by the non-ribosomal thiotemplate mechanism (adapted from

Marahiel, 1997).

More importantly, NRPSs are organised into repeated functional units known as modules, each

of which is responsible for one stage of polypeptide chain elongation leading to the formation

of the final non-ribosomal peptide product (Galm et al., 2008; Cane & Walsh, 1999; Marahiel,

1997). The number of modules within an NRPS generally corresponds to the number of amino

acids present in the structure of the peptide being synthesized and the modules are aligned in

such a way as to be co-linear with the corresponding peptide product (Lautru & Challis, 2004;

Marahiel, 1997). Additionally, each module consists of several structurally independent

domains, with each one catalysing a single reaction step such as activation, substrate

recognition, covalent bonding, optional modification of the incorporated amino acid monomer

and condensation with the amino acid acyl or peptidyl group on the neighbouring module

(Figure 1.5) (Mootz et al., 2002).


19

Figure 1.5 Example of a NRPS assembly line consisting of seven modules responsible for the incorporation

of seven amino acids. Twenty-four chemical reactions are catalysed in the formation of the

final peptide product by twenty-four domains of five different types (C, A, PCP, E and TE)

(Sieber & Marahiel, 2005).

A basic elongation module consists of an adenylation (A) domain, a condensation (C) domain

and a peptidyl carrier protein (PCP) domain. The core of each module is the A domain that is

responsible for the activation of the cognate amino acid as an aminoacyl adenylate through

ATP hydrolysis. The activated substrate is then transferred onto the thiol moiety of the PCP

domain, which subsequently transports the substrate to the C domain. The C domain catalyzes

peptide bond formation between this amino acid substrate and the peptide attached to the PCP

domain of the preceding module, thus elongating the peptide chain. Following peptide bond

formation, the elongated peptide chain is attached to the PCP domain of the downstream

module, where it is passed off and further elongated in the next peptidyltransferase reaction.

The thioesterase (TE) domain, in the termination module, catalyzes the release (and in some

cases oligomerization and/or cyclization) of the mature NRPS-bound peptide product (Figure

1.6) (Bloudoff et al., 2013).


20

Figure 1.6 A simplified example of a typical NRPS assembly line. (1) The cognate amino acids are

activated as aminoacyl-adenylates by the A domains. (2) The aminoacyl-adenylates are

transferred onto the PCP domains. (3) Sequential condensation of the PCP-bound amino acids.

(4) Possibility of modifications of the bound substrate. (5) The peptide chain is transferred from

the terminal PCP domain onto the TE domain via a transesterification reaction. (6) Final product

is released by hydrolysis or macrocyclization. The number of modules and modification

domains varies with each specific multienzyme system (Strieker et al., 2010).

1.4.1 Assembly logic of NRP synthesis

A typical NRPS consists of an initiation, extension and termination module (Figure 1.6). The

minimal NRPS module consists of two catalytic domains and a carrier protein, which together

carry out the selection and activation of the substrate and formation of the peptide bond. These

core domains are the A, C and PCP (otherwise known as the thiolation (T) domain), which

appear in the canonical order C-A-PCP(T) (Figure 1.5). The initiation module does not contain


21

a C domain (Finking & Marahiel, 2004; Mootz et al., 2002). A fourth domain, a thioesterase

(TE), is often found at the C-terminus of the NRPS termination module and catalyzes the

release of the peptide from the NRPS (Felnagle et al., 2008).

Furthermore, in addition to the required domains involved in constructing the peptide

backbone, modules can contain a number of embedded editing/tailoring domains which are

able to create structural diversity by modifying the incorporated amino acid. These auxiliary

domains can act in cis or in trans during the biosynthetic process and examples include

epimerization (E), heterocyclization (Cy), oxidation (Ox), reduction (RE), N-methyltransferase

(MT), communication-mediating (COM) and aminotransferase (AMT) domains (Finking &

Marahiel, 2004).

1.4.1.1 Activation by the Adenylation domain

The A domain is often referred to as the most important domain of each module and this is

because it contains the substrate recognition and ATP-binding sites, which are necessary for

the activation of the specific substrate amino acid and formation of its acyl adenylate through

ATP hydrolysis (Marahiel, 1997).

The A domain selects the cognate amino acid from the available pool of substrates and tethers

it to the PCP domain in a two-step process. Briefly, it first catalyzes the formation of an

aminoacyl-adenylate intermediate through consumption of ATP, which is co-ordinated to Mg2+

and releases inorganic pyrophosphate (PPi) (Figure 1.7). Subsequently, the A domain allows

the transfer of the activated acyl moiety onto the free thiol group on the phosphopantetheinyl

arm of the active holo-PCP domain, thereby releasing AMP and producing a carboxy-thioester-

bound intermediate that is both thermodynamically activated and kinetically labile (discussed

in the following section) (Fischbach & Walsh, 2006; Sieber & Marahiel, 2005; Mootz et al.,

2002).


22

Figure 1.7 The formation of the aminoacyl-adenylate intermediate catalysed by the A domain, at the

expense of ATP (adapted from Marahiel, 2009).

The A domain belongs to the large superfamily of adenylate-forming enzymes, which includes

all A domains of modular peptide synthetases and distinct proteins such as acetyl-CoA

synthetases, luciferases, oxidoreductases and 4-coumaryl CoA ligases. All of these enzymes

possess the ability to activate their carboxylic acid or amino acid substrates to their acyl

adenylates at the expense of ATP (Konz & Marahiel, 1999; Marahiel, 1997). They all share a

homologous domain of approximately 550 amino acids that consists of a set of highly

conserved signature sequences, which have been shown to be the major determinants of the

substrate specificity exhibited by A domains (Marahiel, 1997).

The determination of the crystal structures of two members of this adenylate-forming enzyme

superfamily, firefly luciferase of Photinys pyralis and the phenylalanine-specific A domain of

the gramicidin S synthetase (GrsA) of Bacillus brevis, termed PheA, provided fundamental

insight into the structural basis of substrate recognition and activation (Finking & Marahiel,

2004; Stachelhaus et al., 1999; Conti et al., 1997; Marahiel, 1997). Furthermore, it was

observed that even though the protein sequence similarity between PheA and the firefly

luciferase is only 16 %, the enzymes share a highly conserved three-dimensional structure. It

can be expected that very similar three-dimensional structures would be observed for all A

domains of peptide synthetase origin that show 30-60 % sequence identity to PheA (Marahiel,

1997).

The A domain of GrsA folds into a large amino-terminal and a smaller carboxy-terminal

subdomain. An ordered layer of water molecules mediate interactions between the two sub-


23

domains. Ten highly conserved core motifs which surround the active site where the substrate

binds are associated with the amino-terminal domain, however, a lysine residue located in the

carboxy-terminal domain provides an essential interaction in co-ordinating the α-carboxyl

group of the substrate amino acid (Sieber & Marahiel, 2005; Stachelhaus et al., 1999).

The conserved motifs serve as functional anchors and it has been shown that many of the amino

acid residues within these motifs perform a key role in the co-ordination of ATP binding and

hydrolysis, as well as adenylation of the specific substrate carboxy moiety (Sieber & Marahiel,

2005; Stachelhaus et al., 1999). It has, however, been observed that some A domains display

“relaxed” substrate specificity and in these cases, chemically or sterically similar amino acids

are also recognised and analogously processed (Keating & Walsh, 1999).

1.4.1.2 Transport of substrates and intermediates to the catalytic centres by the

Peptidyl Carrier Protein

Located downstream of the A domain, the equally important PCP domain is approximately 80-

100 amino acid residues in length and is highly homologous to the acyl carrier protein (ACP)

involved in fatty acid synthases (FASs) and polyketide synthases (PKSs) (Sieber & Marahiel,

2005). Carrier proteins, also referred to as thiolation domains, may either be freestanding or

embedded in enzymatic systems. A variant of the carrier protein commonly found in

siderophore NRPS systems, is the aryl carrier protein (ArCP) (Qiao et al., 2007). The carrier

proteins are tasked with keeping reaction intermediates bound to the enzymatic machinery and

are responsible for transportation of substrates and elongation intermediates to the catalytic

centres of the PKS, NRPS or FAS assembly lines (Qiao et al., 2007; Stachelhaus et al., 1996).

In order for the PCP to become functional, each inactive apo-PCP domain must be post-

translationally modified (“primed”) by a phosphopantetheinyl transferase (PPTase), which

involves the transfer of the cofactor, 4’-phosphopantetheine (4’-PP), from coenzyme A (CoA)

to a conserved serine residue on the PCP domain. The PPTase stimulates the nucleophilic

attack of the PCP serine hydroxyl group on the pyrophosphate bridge of CoA, resulting in the

transfer of 4'-PP to the PCP domain and release of 3',5'-ADP (Lambalot et al., 1996). This, in

turn, results in an active holo-PCP domain with a flexible phosphopantetheinyl arm that is able

to covalently bind both the amino acyl and peptidyl substrates as energy-rich thioesters (Figure


24

1.8) (Fischbach & Walsh, 2006; Schwarzer et al., 2003). The PCP-domain is then able to act

as the transport unit which enables the activated amino acids and elongation intermediates to

move between all of the catalytically active entities, as the A and C domains associate closely

to form a catalytic platform onto which the PCP domain is flexibly tethered between their active

sites (Tanovic et al., 2008).

Figure 1.8 Modification of the PCP domain by a phosphopantetheinyltransferase (PPTase). The transfer

of the 4’- phosphopantetheine cofactor from coenzyme A to a conserved serine residue in the

PCP domain is catalysed by members of this enzyme class (adapted from Fischbach & Walsh,

2006).

1.4.1.3 Peptide elongation by the Condensation domain

The C domain is approximately 450 amino acids in length and is responsible for the elongation

of the peptidyl chain. C domains are normally localized between each consecutive A-PCP

domain and catalyse the condensation reaction between the peptidyl chain tethered to the

phosphopantetheinyl arm of the upstream PCP domain and the amino acid bound to the

downstream PCP domain (Lautru & Challis, 2004). However, in the first condensation reaction

of an NRPS, both these reaction intermediates would typically be aminoacyl groups attached

to their respective PCP domains. Furthermore, C domains are absent from modules involved

in peptide initiation (Mootz et al., 2002).


25

There is little information concerning the exact mechanism of peptide elongation and how the

interaction of modules affects the direction of polymerization, but it is thought that peptide

bond formation proceeds via the nucleophilic attack of the free α-amino group on the

downstream PCP-bound acceptor amino acid on the activated carboxy-thioester of the

upstream PCP-bound donor amino acid (Figure 1.9). This reaction facilitates the translocation

of the growing peptide chain onto the next module for elongation and structural changes

(Bloudoff et al., 2013; Sieber & Marahiel, 2005; Mootz et al., 2002; Marahiel, 1997).

Moreover, this condensation reaction is strictly unidirectional, leading to a downstream-

directed synthesis of the NRPS product (Samel et al., 2007).

Figure 1.9 Peptide elongation catalysed by the C domain, which involves an attack of the nucleophilic

amine of the acceptor substrate onto the electrophilic thioester of the donor substrate (Sieber &

Marahiel, 2005).

In order to shed light on the catalytic mechanism of the C domain, three structures that contain

NRPS C domains have been determined by X-ray crystallography, including a stand-alone C

domain (Keating et al., 2002), a C-PCP didomain complex (Samel et al., 2007) and a C-A-

PCP-TE termination module (Tanovic et al., 2008). The overall architecture of the C domain

revealed a pseudodimeric configuration consisting of both an N-terminal and C-terminal

subdomain. The active site is located at the bottom of a “canyon” or “V-shape” formed by the

two subdomains and is covered by a “latch” that crosses over from the C to N subdomain


26

(Figure 1.10) (Bloudoff et al., 2013; Marahiel, 2009; Finking & Marahiel, 2004). The catalytic

centre includes a conserved HHxxxDGxS core motif (where x is any amino acid and defined

residues are represented by the single-letter amino acid code), that is also found in

dihydrolipoyl transacetylases, chloramphenicol acetyltransferases, and NRPS epimerization

and Cy domains (Sieber & Marahiel, 2005; Keating & Walsh, 1999; Marahiel et al., 1997). A

model, supported by mutational studies, suggests that the second histidine of this motif, which

is located at the bottom of the canyon, may act as a catalytic base promoting the deprotonation

of the NH3+ moiety of the thioester-bound nucleophile prior to peptide bond formation.

However, recent pK value analysis of this active site residue suggests that peptide bond

formation may depend mainly on electrostatic interactions rather than a general acid/base

catalysis (Marahiel, 2009; Samel et al., 2007; Konz & Marahiel, 1999).

Figure 1.10 Structure of the PCP-C didomain from the surfactin synthetase illustrating the active site

histidine (His) residue located on the floor of the C-domain “canyon” (Marahiel, 2009).


27

1.4.1.3.1 Heterocyclization domains

The C domain of a module, which catalyzes basic peptide bond formation only, can be replaced

by a specialised heterocyclization (Cy) domain that shares striking structural and functional

homology to the C domain. The Cy domain combines the condensation function of the C

domain with additional heterocyclization and dehydration functions using the side chains of

the amino acids cysteine, serine or threonine within the product peptide backbone to produce

thiazoline (from cysteine), oxazoline (from serine) or 5-methyloxazoline (from threonine)

heterocycles (Walsh et al., 2001).

Cy domains were first identified in 1997 in the cyclic dodecylpeptide antibiotic bacitracin

synthetase, produced by Bacillus licheniformis ATCC 10716 (Konz et al., 1997) and were

further validated in the biochemical characterisation of yersiniabactin, an iron-chelating

virulence factor of Yersinia pestis (Gehring & Walsh, 1998). The catalytic core motif,

HHxxxDGxS, of the C domain is modified to DxxxxDxxS in the Cy domain. The conserved

aspartate residues are critical for both condensation and heterocyclization (Keating et al., 2002;

Keating & Walsh, 1999). Examples of secondary metabolites produced using Cy domains are

epothilone A, myxothiazol and mycobactin A produced by Sorangium cellulosum So ce90,

Stigmatella aurantiaca DW4/3-1 and M. tuberculosis, respectively (Figure 1.11) (Duerfahrt et

al., 2004).


28

Figure 1.11 Heterocyclic ring-containing secondary metabolites from various organisms (the five-

membered thiazole and oxazole rings are shaded grey) (Duerfahrt et al., 2004).

The first reaction step catalysed by Cy domains is peptide bond condensation, carried out by

the nucleophilic attack of a PCP-bound cysteine, serine or threonine acceptor substrate onto

the thioester of the donor substrate. The next step involves the nucleophilic attack by the

hydroxyl side chain of serine/threonine or thiol side chain of cysteine onto the carbonyl C atom

of the newly-formed peptide bond to yield hemiaminal or thiohemiaminal intermediates and

the five-membered heterocyclic ring. The intermediates are subsequently dehydrated to yield

the C=N bond and the final oxazoline or thiazoline product (Figure 1.12) (Sieber & Marahiel,

2005; Walsh et al., 2001). In non-ribosomal peptide products such as the glycopeptide

antibiotic, bleomycin (produced by ‘Streptomyces verticillatus’ ATCC 15003) or myxothiazol,

additional oxidation (Ox) domains convert these heterocycles into more stable oxazole or

thiazole rings. Heterocyclic rings are common structural features of NRPs and are important

for the interaction with proteins, DNA and RNA, as well for chelating metal ions (Walsh,

2004).


29

Figure 1.12 The formation of thiazoline (top of figure) and oxazoline heterocycles (bottom of figure) from

cysteine and threonine precursors, respectively (Walsh et al., 2001).

1.4.1.4 Peptide release by the Thioesterase domain

The termination of peptide synthesis on an NRPS assembly line is catalysed by the terminal

enzyme of the last module. During synthesis, the growing peptide chain is transported from

one module to the next until it reaches the final module’s PCP domain. Product release is then

achieved by the catalytic action of a C-terminal TE domain, which occurs when the nascent

peptidyl chain is transferred from the terminal PCP to a highly conserved active site serine

residue present in the TE domain to generate a covalent acyl-enzyme intermediate. This

intermediate can then be released by the external nucleophile, water, in a hydrolysis reaction

to form a linear acid or by the predominant mechanism of regio- and stereoselective

intramolecular macrocyclization using an internal nucleophile to produce a cyclic peptide

(Figure 1.13) (Sieber & Marahiel, 2005; Mootz et al., 2002). Macrocyclization is believed to

be favoured due to the fact that cyclic products are more resistant to proteolytic cleavage. In


30

addition, TE domains that catalyse a cyclization reaction are also referred to as peptide cyclases

(Marahiel, 2009; Sieber & Marahiel, 2005; Finking & Marahiel, 2004).

The crystal structures of several dissected TE domains has revealed the presence of the

common fold of α/β-hydrolases, such as lipases and esterases, as well as the fact that the active

site consists of a catalytic triad composed of serine at position 80 (Ser80), histidine at position

207 (His207) and aspartate at position 107 (Asp107). Within this triad, the serine residue

serves as the site of tetrahedral intermediate formation that is stabilized by an oxyanion hole

en route to the acyl-enzyme intermediate. This intermediate is attacked by the action of an

internal nucleophile of the peptide chain (which can be the N-terminal amino group or a

functional side chain) or water, which results in a macrocyclic product or linear peptide,

respectively. It remains uncertain as to how the active site is sufficiently sealed from water in

order to catalyse cyclization rather than hydrolysis. However, the structures of the TE domains

have also revealed a flexible “lid” region that may possibly adopt an open conformation for

substrate entry and a closed conformation for excluding water from the active site (Condurso

& Bruner, 2012; Marahiel, 2009; Schwarzer et al., 2003).

Figure 1.13 Illustration depicting peptide release by the TE domain. Product release can be achieved either

by the external nucleophile, water, to produce a linear acid product as observed in (A) or by an

internal nucleophile to produce a cyclic product as observed in (B) (Sieber & Marahiel, 2005).


31

1.4.1.5 Editing/tailoring domains

In addition to the essential domains found in every NRPS, further modifications to the final

product can be achieved by the action of several editing/modifying domains that act to increase

the diversity of NRPs. These so-called modifying domains are not present in every NRPS

system, but are nevertheless vital for the proper processing of their designated substrate within

their respective synthetase. Inactivation or deletion of these domains usually results in the

synthesis of products with severely reduced or no bioactivity.

1.4.1.5.1 Methylation

Certain non-ribosomal peptides such as cyclosporin, enniatin, actinomycin and yersiniabactin

possess N-methylated or C-methylated peptide bonds. These modifications are introduced by

a methyltransferase (MT) domain, embedded within the canonical fold of an associated A

domain, thus making the peptide less susceptible to proteolytic degradation. The MT domain,

including both N- and C-methyltransferases, is able to catalyse the transfer of the S-methyl

group from S-adenosylmethionine (SAM) to the α-amino group of the thioesterified aminoacyl

intermediate in C-A-MT-PCP modules, thereby releasing S-adenosylhomocysteine as a

reaction byproduct (Figure 1.14) (Fischbach & Walsh, 2006; Sieber & Marahiel, 2005; Finking

& Marahiel, 2004).

Figure 1.14 The MT domain catalyzes the transfer of the CH3 (Me) group from SAM to the amino group

of the aminoacyl-S-intermediate prior to peptide formation with the upstream peptidyl chain

(Walsh et al., 2001).


32

1.4.1.5.2 Epimerization (control of stereochemistry)

A prevalent structural feature of NRPs is the incorporation of the less common D-amino acids.

Two different strategies are utilized by NRPSs for their incorporation, which may be

accomplished simply by an A domain with exclusive specificity towards a D-amino acid or by

epimerization of L-amino acids by integrated epimerization (E) domains (Sieber & Marahiel,

2005). The E domains are found on the carboxy terminus of the respective module’s PCP

domain and catalyse the racemization of the PCP-bound amino acid or of the C-terminal amino

acid of the growing peptidyl chain. Two different types of E domains catalyse these reactions

and are known as either aminoacyl epimerases, which can only be part of initiation modules,

or peptidyl epimerases, which are part of elongation modules. Due to the fact that E domains

are only involved in catalyzing the racemization of their substrates, specific incorporation of

the D-amino acid into the growing peptide chain is achieved by the enantiomer-selective donor

site of the downstream C domain. The C domain therefore acts as a type of “filter”, which

selectively withdraws the correct enantiomer from the pool of L/D-amino acids (Schwarzer et

al., 2003). In some rare cases, such as in the arthrofactin synthetase found in Pseudomonas sp.

MIS38, the C domain itself also exhibits epimerization activity in addition to its normal

function and it is then known as a “dual C/E” domain (Balibar et al., 2005).

1.4.1.5.3 Reduction domain

A reduction (RE) domain replaces the TE domain in a few NRPS systems, such as in the

biosynthesis of gramicidin A in B. brevis and safracin in Pseudomonas fluorescens. RE

domains, such as those found in the biosynthesis of myxochelin A in Angiococcus disciformis,

catalyse an alternative mechanism of peptide release that involves the NADPH-dependent

reduction of the PCP-bound peptidyl thioester to yield an unstable thioacetal intermediate that

is converted into a linear aldehyde or alternatively into an alcohol via a second reduction of the

thioacetal group (Figure 1.15) (Velasco et al., 2005; Gaitatzis et al., 2001). Another rare type

of chain termination strategy is found in some NRPSs, where the RE domain triggers the

reductive release, via nucleophilic attack by the free N-terminal amino group, of a highly

reactive peptide aldehyde that results in the subsequent formation of a stable macrocyclic imine

(Kopp & Marahiel, 2007). RE domains are also known to catalyse the NADPH-dependent


33

reduction of thiazoline into thiazolidine by the addition of two electrons, as witnessed in one

of the rings in yersiniabactin (Sieber & Marahiel, 2005; Velasco et al., 2005).

Figure 1.15 The RE domain reduces the C-terminal carboxy-group to an aldehyde or to the corresponding

alcohol using NADPH as cofactor (Schwarzer et al., 2003).

1.4.1.5.4 Oxidation domain

Oxidation (Ox) domains often appear in the same module as a Cy domain in order to catalyze

the oxidation of the hydrolytically labile dihydroheterocyclic thiazolines and oxazolines by

two-electron transfer to yield stable heteroaromatic thiazole or oxazole rings (Figure 1.16)

(Duerfahrt et al., 2004; Schwarzer et al., 2003). Ox domains can be localized in the

accompanying A domain, as is the case in the epothilone synthetase, or they can be

C-terminally fused to the PCP domain of the respective module, as witnessed in the bleomycin

synthetase (Schwarzer et al., 2003; Du et al., 2000). Furthermore, flavin mononucleotide

(FMN) has been verified as a cofactor of Ox domains. FMN is reduced to FMNH2 during the

oxidation of the substrate and is subsequently re-oxidised by the reduction of molecular oxygen

to superoxide. While the oxidation of thiazoline to thiazole in the epothilone synthetase is

catalysed in cis by an FMN-containing Ox domain (a corresponding in cis flavoprotein domain

exists in the bleomycin synthetase), a second trans-acting Ox domain has been proposed to be

involved in the formation of the second thiazole ring found in the structure of bleomycin A2

(Finking & Marahiel, 2004; Du et al., 2000). The fact that these enzymes are able to act in

trans, where they are able to recognise the peptidyl chains on NRPS modules by protein-protein


34

interactions, is testament to the enormous structural variation created in these natural products

(Walsh et al., 2001).

Figure 1.16 FMN-containing Ox domains catalyze the two electron oxidation of thiazolines and oxazolines

to yield stable heteroaromatic thiazole or oxazole rings, respectively (Schwarzer et al., 2003).

1.4.1.5.5 Further modifications

In the case of the linear gramicidin A, the N-terminus of the non-ribosomal peptide possesses

a formyl group which is introduced by a formylation (F) domain, localized N-terminal to the

A domain of the initiation module. The F domain is responsible for the N-formylation reaction

by means of the cofactor N-formyltetrahydrofolate. Other formylated NRPs include

coelichelin, whose ornithine residues are believed to be N-formylated in trans and

anabaenopeptilide 90-A whose N-terminus exhibits an N-formylated glutamine residue (Lautru

et al., 2005; Sieber & Marahiel, 2005).

Surfactin and fengicin are lipopeptides, which represent a subgroup of NRPs whose peptide

backbones are N-terminally bound to a fatty acid. An N-terminal C domain, in addition to the

A and PCP domain, is usually present in the initiation module of these NRPSs and is thought

to catalyse bond formation to the fatty acid.

An aminotransferase (AMT) domain exists within the mycosubtilin NRPS that converts a

thioesterified β-ketoacyl intermediate to a covalently tethered β-aminoacyl thioester with


35

simultaneous removal of the α-amino group of glutamine to form α-keto-glutamine in a

variation of the classic transamination reaction. It was therefore proposed to be responsible for

the transfer of an amine group to the β-position of the growing acyl chain. The ability to

incorporate amine functionality directly into NRPs creates a functional handle for

macrocyclization strategies and acts as a potent hydrogen bond donor, which can significantly

alter the biology of a given compound (Fischbach & Walsh, 2006).

All of the modifications that have been introduced thus far are catalysed by domains that are

embedded into their respective NRPS modules and almost entirely affect only the peptide

backbone. Additionally, certain enzymes such as glycosyl transferases, halogenases and

hydroxylases are able to modify the peptide’s side chains and are generally encoded in the same

biosynthetic gene cluster.

1.4.2 NRPS substrate specificity prediction and the non-ribosomal code

The A domain has been described as the most important domain within each NRPS module

due to the fact that it recognizes and activates only the cognate substrate amino acid as its acyl

adenylate (using ATP to drive the reaction). Hence A domains act in a ‘lock and key’ process

and are considered the primary determinant of substrate specificity, thereby also defining what

molecules can be synthesized by the specific NRPS (Lautru & Challis, 2004; von Döhren et

al., 1999). Knowledge about how A domains are able to recognize their specific substrates is

of fundamental importance to understanding and manipulating these complex enzymatic

systems for use as scaffolds for combinatorial biosynthesis. Combinatorial biosynthesis

(section 1.4.4) could allow for the generation of novel derivatives of the non-ribosomal peptide

and ideally new, more potent antibiotics (Rausch et al., 2005; Lautru & Challis, 2004; Challis

et al., 2000; Conti et al., 1997).

The study of A domain specificity was greatly facilitated by the determination of the crystal

structure of firefly luciferase and the phenylalanine activating domain, PheA, from the first

module of gramicidin synthetase (GrsA). The co-crystalization of PheA in a ternary complex

with L-phenylalanine (L-phe) and AMP allowed the discovery of ten highly conserved motifs,

denoted A1 to A10, which extend over a region of 450 amino acids and mostly surround the

active site where the substrate binds. The identification of this hydrophobic L-phe binding


36

pocket and the A domain residues making contact with L-phe provided a structural basis for

understanding the specificity of peptide synthetases such as NRPSs (Rausch et al., 2005; Lautru

& Challis, 2004; Challis et al., 2000; Conti et al., 1997).

Expanding on the approach pursued by Conti and colleagues, Stachelhaus et al. (1999) and

Challis et al. (2000) compared the L-phe binding pocket of GrsA with the corresponding

sequences of over 150 aminoacyl and iminoacyl adenylate-forming domains of NRPSs to

pinpoint the essential amino acid residues involved in substrate specificity and binding. Both

studies examined a ~100 amino acid stretch between the core motifs A4 and A5 and identified

10 amino acid residues that were within approximately 5.5 Å of the active site-bound

phenylalanine and in contact with the substrate (Rausch et al., 2005; Lautru & Challis, 2004;

Conti et al., 1997).

These 10 amino acid residues were determined to be crucial for substrate binding and catalysis,

as alignments of consensus A domain residues to the PheA domain revealed that all A domains

display the same type of binding pockets, with different key residues that interact with different

amino acid substrates. It was postulated that two residues, Asp235 and Lys517, stabilize the α-

amino group of the amino acid substrate via two hydrogen bonds and are critical for the correct

positioning of the substrate within the active site for ATP-dependent activation. These two

residues are located in the conserved core motifs of A4 (Asp235) and A10 (Lys517). The other

residues bordering the PheA specificity binding pocket were determined to be Ala236, Ile330

and Cys331 on the one side and Ala322, Ala301, Ile299 and Thr278 on the other side of the

pocket. Both sides are separated by the indole ring of tryptophan at position 239 (Trp239),

which is located at the bottom of the pocket (Stachelhaus et al., 1999).

More importantly, it was determined that due to the high degree of sequence identity shared

between NRPS A domains, the amino acid residues that correspond to those lining the PheA

binding pocket could be used to reveal substrate specificity in other A domains. The

consecutive order of the 10 residues was determined to constitute the signature sequence

involved in the binding pockets of A domains and can be interpreted as the “specificity-

conferring code” (also referred to as the non-ribosomal code), as it allows for the prediction of

A domain selectivity on the basis of the A domain primary sequence (Figure 1.17) (Table 1.1)

(Rausch et al., 2005; von Döhren et al., 1999).


37

Figure 1.17 A multiple sequence alignment of the primary amino acid sequences from known A domains in

order to determine the selectivity-conferring residues (a). The sequence of ~100aa between the

core motifs A4 and A5 from PheA from GrsA was aligned with the corresponding sequence of

AspA from the surfactin synthetase, SrfA, OrnA from the gramicidin synthetase, GrsB3 and

ValA from the cyclosporine synthetase. Yellow residues indicate those involved in the binding

pocket positions and brown residues indicate conserved motifs which anchor the alignment. (b)

Ten highly conserved residues were extracted from the sequence alignment and the consecutive

order of the amino acids was determined to constitute the signature sequence involved in the

binding pockets of the aligned A domains. The missing residue, Lys517, is highly conserved

within motif A10, which is not shown in the protein sequence. The alignment was extended to

160 different A domains to confirm accuracy in determining the signature sequence (adapted

from Stachelhaus et al., 1999).

This discovery confirmed previous findings from site-directed mutagenesis and photoaffinity

labelling experiments that indicated that these amino acid residues were involved in ATP

binding and hydrolysis (Gocht & Marahiel, 1994; Pavela-Vrancic et al., 1994). The non-

ribosomal code was initially restricted to amino acid-activating A domains but was extended

to carboxy acid-activating A domains when the crystal structure of the stand-alone 2,3-

dihydroxybenzoic acid activating domain, DhbE, from Bacillus subtilis was solved (May et al.,

2002).


38

Table 1.1 Consensus specificity code for substrates from several adenylation domains

Clusters of signature sequences extracted from A domains activating the same substrates were used to determine

the consensus sequences for the recognition of several amino acid substrates. The biosynthetic template from

which each A domain specificity code was derived is included, along with the overall similarity of each signature

sequence. Variable constituents within each codon are represented by red residues and ‘wobble’-like positions,

which reveal a large degree of variability throughout all codons, are indicated in blue. Aad, δ(L-α-aminoadipic

acid); Dab, 2,3-diamino butyric acid; Dhb, 2,3-dihydroxy benzoic acid; Sal, salicylate; Phg, L-phenylglycine;

hPhg, 4-hydroxy-L-phenylglycine; Pip, L-pipecolinic acid; Dht, dehydrothreonine; ‘@’ indicates a modification

of the residue (Stachelhaus et al., 1999).


39

The successful mutation of all the key residues of the PheA binding pocket, which resulted in

relaxation or alteration of its substrate specificity, demonstrated the reliability of the non-

ribosomal code. This has resulted in the development of web-based NRPS prediction services

such as the NRPS-PKS knowledge base (Ansari et al., 2004), NP.searcher (Li et al., 2009),

PKS/NRPS analysis (Bachmann & Ravel, 2009) and antiSMASH 3.0 (Weber et al., 2015),

which make use of the “specificity-conferring code” to predict putative A domain substrates in

NRPS genes. Although these tools have been relatively successful at predicting the specificities

of A domains in new NRPS genes, they do have a number of weaknesses (Challis et al., 2000).

A clear shortcoming is that predictions of substrate specificities are based on known A domain

sequences. Since not all A-domain sequences in nature are known and, in particular, since there

are relatively few sequences for A domains that bind more unusual substrates, the accuracy of

substrate specificity prediction is limited. The specificity of uncharacterised A domains must

therefore be deduced from the available code for domains with known specificity. It has been

observed that there are deviations from the code. For example, not all A domains specific for

phenylalanine have the exact same specificity binding pocket sequence as GrsA, e.g. BarG of

the barbamide synthesis gene cluster from Lyngbya majuscula (GenBank accession number:

AAN32981) has DAWTVAAVCK instead of DAWTIAAICK. In addition, there are examples

of codes where the predicted substrate specificity does not correspond to the actual activated

amino acid, such as in the alanine-activating domain Sare0718 from the marine actinomycete

Salinispora arenicola CNS-205 (which has the code for valine) and in the biosynthetic cluster

for fusaricidin, a mixture of 12 depsipeptides from Paenibacillus polymyxa PKB1, which

displays relaxed substrate specificity and allows for the incorporation of D-amino acids instead

of their L-isomers (Xia et al., 2012; Li & Jensen, 2008).

A further shortcoming has been observed in the analysis of the active sites within the A domains

of certain types of NRPSs, particularly those belonging to fungi, as the GrsA crystal (from a

bacterium) seems to be an inadequate model for fungal NRPSs or because the large number of

sequence variants in the active site of fungal NRPSs does not allow for the identification of the

key residues required for substrate-specificity prediction (Prieto et al., 2012). Certain positions

are considered more variable or ‘wobble’-like than others, particularly 239, 278, 299, 322 and

331, which are highly variant. Furthermore, positions 235 and 517 are considered invariant

and positions 236, 301 and 330 are moderately variant (Table 1.1). The variability reflects

each position’s importance in contributing to substrate specificity, but also causes dissimilarity


40

between the signature sequences for A domains specific for identical substrate amino acids

(Stachelhaus et al., 1999).

It is due to these limitations that Rausch et al. (2005) expanded on the work of Stachelhaus et

al. (1999) and Challis et al. (2000) by publishing a machine learning algorithm in which

transductive support vector machines (TSVMs) were utilised to statistically propose NRPS A

domain specificity using the physico-chemical fingerprint of the residues within 8 Å of the

active site of the A domain (a total of 34 residues). The residues are encoded into TSVMs

based on their physico-chemical properties such as the number of hydrogen bond donors,

polarity, volume, secondary structure preferences, hydrophobicity and isoelectric point and a

continuously updated dataset of A domains with known specificity are used in predicting

substrate specificity. Due to the occurrence of relaxed/promiscuous specificity in certain A

domains, such as in the NRPS responsible for xenematide biosynthesis in Xenorhabdus

nematophila, the specificities for substrates with similar physico-chemical properties are

clustered together (Crawford et al., 2011; Rausch et al., 2005).

An open source web-based predictor, NRPSpredictor, based on TSVMs, was built on the 34

active site residues in order to predict A domain specificity, which was later refined and

replaced by the NRPSpredictor2, which possesses improved prediction performance, two new

prediction levels and a larger database (Rottig et al., 2011).

Although the TSVM-based method was based on a more recent database and was able to

provide a substrate-specificity prediction in an additional 18% of cases, it is still beneficial to

use it in combination with the empirical predictive method developed by Stachelhaus et al.

(1999) and Challis et al. (2000) in order to create an even more accurate prediction tool (Rausch

et al., 2005). This is largely due to the fact that most of the weaknesses of the older method

remain and by expanding the number of residues considered, it may have amplified the

problems associated with including data with little or no influence on the specificity of the A

domains. In addition, the clustering of specificities reduces the accuracy of the predictions

and, although this is acceptable for A domains which possess relaxed specificity, other A

domains are much more specific. There is currently no way to distinguish a highly specific A

domain from a relaxed one (Rausch et al., 2005; Mootz et al., 2002; Challis et al., 2000).


41

This situation prompted interest in developing new prediction methods supported by other

approaches, such as the use of hidden Markov Models (HMM). Khurana et al. (2010) applied

HMM to functionally classify the acyl-CoA synthetase superfamily members. The results of

this work suggest that the application of HMM to classify this superfamily outperforms the

predictions based on a restricted number of active site residues (Khurana et al., 2010).

Furthermore, a novel two-mode factor analysis model based on latent semantic indexing (LSI)

has recently been published by Baranasic et al. (2013). This model is able to predict the specific

amino acid that is activated by the A domain in contrast to a cluster of similar amino acids.

The authors suggest that a detailed comparison of prediction quality against those of the

NRPSpredictor, showed that the LSI model performed slightly better and is thus the most

accurate method currently available for prediction of A domain substrate specificities

(Baranasic et al., 2013).

1.4.3 NRPS biosynthetic strategies

The order in which the modules of an NRPS are utilised to construct the final product and the

assembly of the core domains within each module can vary considerably, thereby allowing

these enzymatic systems to synthesize diverse chemical structures. The three most common

biosynthetic strategies employed by NRPSs include the linear or type A NRPS, iterative or

type B NRPS and the nonlinear or type C NRPS (Mootz et al., 2002).

The simplest biosynthetic strategy is that of the linear or type A NRPSs, in which the three core

domains are arranged in the order C-A-PCP in an elongation module, which is able to add one

amino acid to the growing peptide chain (Figure 1.18). The initiation module is responsible

for incorporating the first amino acid of the peptide chain and does not contain a C domain,

whereas, the termination module contains a TE domain in order to catalyse the release of the

final product. Therefore, a typical, linear NRPS template consists of n modules with a domain

organization in the order of A-PCP-(C-A-PCP)n-1-TE, for construction of a final peptide chain

containing n amino acids. The sequence of the final peptide chain is determined exclusively

by the number and order of the modules, which differs in the case of nonlinear and iterative

NRPSs. Examples of linear NRPSs include those involved in the biosynthesis of cyclosporin,

surfactin, actinomycin, peramine, ergovaline, tyrocidine and δ-(L-α-aminoadipyl)-L-cysteinyl-

D-valine (ACV), the isopenicillin and cephalosporin precursor (Mootz et al., 2002).


42

Figure 1.18 Example of the module and domain organization, A-PCP-(C-A-PCP)n-1-TE, observed in a linear

or type A NRPS, such as the ACV synthetase, which synthesizes the isopenicillin precursor

ACV (Mootz et al., 2002).

In the iterative or type B NRPSs, modules are used more than once in an efficient method of

assembling multimeric peptide products. Instead of replicating the elongation modules, the

entire NRPS is used repeatedly in an iterative manner to construct peptide chains that consist

of recurring, short sequences. The product produced by the first cycle of synthesis is stalled

on the C-terminal TE domain, thereby regenerating the NRPS for the assembly of the next

product of the same amino acid sequence. Oligomerization of the completed product occurs

on the TE domain and is released via hydrolysis or macrocyclization, with the latter being the

preferred method. Examples of iterative NRPSs are those that synthesize enterobactin (Figure

1.19), gramicidin, enniatin and bacillibactin (Mootz et al., 2002).

The final biosynthetic strategy is known as the nonlinear or type C NRPS, which can, in most

cases, be identified from their primary sequence due to the fact that the identified module and


43

domain organization will deviate from the classical C-A-PCP domain organization. They are

also characterized by their ability to incorporate small soluble molecules that are not covalently

tethered to the NRPS template during synthesis, such as the involvement of amines in

vibriobactin biosynthesis, instead of PCP-loaded amino acids (Finking & Marahiel, 2004;

Keating et al., 2002). Due to the fact that amines, such as norspermidine in vibriobactin

biosynthesis, lack a carboxyl group necessary for their covalent attachment as a thioester,

specialized C domains are employed to incorporate amines. The vibriobactin biosynthetic

cluster also encodes an unusual tandem arrangement of Cy domains, in which one is

responsible for heterocyclic ring formation, while the other’s function remains unclear (Mootz

et al., 2002). Furthermore, unusual internal cyclizations are often associated with deviations

from the standard domain organization observed in linear NRPSs, such as in the biosynthesis

of bleomycin (Mootz et al., 2002).

Other unusual biosynthetic strategies employed by type C NRPSs include utilizing a single

domain to catalyse multiple different reactions, such as the cysteine-specific A domain in the

yersiniabactin biosynthetic machinery, which is responsible for the loading of three different

PCPs (Suo et al., 2001), as well as the existence of a one-domain NRPS involved in the

biosynthesis of the antibiotic novobiocin in Streptomyces spheroides. The enzyme, NovL,

shares homology with acyl-adenylate forming enzymes of the same superfamily as A domains

and catalyzes formation of the peptide bond between 3-dimethylallyl-4-hydroxybenzoic acid

and 3-amino-4,7-dihydroxy-8-methyl coumarin in a reaction that is similar to those catalysed

by acyl-CoA ligases. NovL is able to activate the carboxy acid of 3-dimethylallyl-4-

hydroxybenzoic acid towards the acyl adenylate, but instead of transferring it onto a PCP

domain, the acyl adenylate acts as the electrophile for the condensation with the amino group

nucleophile of 3-amino-4,7-dihydroxy-8-methyl coumarin (Mootz et al., 2002). It is also

interesting to note that free-standing A domains are known to activate aromatic carboxylic

acids and transfer (acylate) them to ArCPs, which are fused to isochorismate lyase, an enzyme

involved in the synthesis of 2,3-dihydroxybenzoic acid, which is used as a starter unit in this

type of synthetase (Crawford et al., 2011; Schmoock et al., 2005).


44

Figure 1.19 Example of the iterative or type B NRPS as observed in the biosynthesis of enterobactin. Three

Dhb-Ser-S-ppant intermediates are produced on the two modules of the enterobactin NRPS and

oligomerized and cyclized on the TE domain (Mootz et al., 2002).

Additionally, fragments of NRPS assembly lines such as A-PCP didomains or separate, but

adjacently encoded A and PCP domains are found in the absence of any other NRPS machinery

(Fischbach & Walsh, 2006; Ullrich & Bender, 1994). It was discovered that these A-PCP

didomains and freestanding A/PCP domains do in fact activate a specific L-amino acid as an

aminoacyl adenylate, which then acts as a substrate for a partner enzyme to chemically modify

the β-or γ-carbon of the thioesterified aminoacyl intermediate. Consequently, it has been

inferred that the use of didomains or freestanding domains is a strategy to sequester a portion


45

of the pool of proteinogenic amino acids in order to modify them into a nonproteinogenic form,

which can be used in the biosynthesis of extremely diverse secondary metabolites (Fischbach

& Walsh, 2006).

The nonlinear NRPSs are impressive examples of how microbial producers are able to modify

assembly-line organizations and operations in order to evolve novel combinations of the

enzymatic components to generate new natural products (Fischbach & Walsh, 2006; Schwarzer

et al., 2003).

1.4.4 Combinatorial biosynthesis and intermolecular communication

Combinatorial biosynthesis can be defined as ”the application of genetic engineering to modify

biosynthetic pathways to natural products in order to produce new and altered structures using

nature’s biosynthetic machinery” (Floss, 2006). In this approach, which was first demonstrated

in work by David Hopwood and colleagues (Hopwood et al., 1985), biosynthetic genes are

cloned into an actinomycete host that does not naturally produce the antibiotic. Selected genes

in the gene cluster are then deleted or replaced with carefully-chosen antibiotic biosynthetic

genes from the producers of other actinomycete antibiotics, so that the host strain produces a

chemical derivative of the original antibiotic (i.e. a hybrid antibiotic), dictated by the

composition of the modified biosynthetic gene cluster (Weissman & Leadlay, 2005; Reynolds,

1998).

The order and domain composition of NRPS modules are the direct consequence of a

meticulous selection process during evolution to synthesize a peptide molecule with particular

bioactive properties. Once the logic and mechanisms of NRPS assembly had been investigated,

interest developed in the rational manipulation of the NRPS template to synthesize novel

peptide products (Sieber & Marahiel, 2005). Subsequently, over the past decade and a half,

several strategies have been developed to redesign NRPS assembly lines in order to generate

peptides with altered biological properties. Most of these exploits have focussed on the

combinatorial approach of swapping or deleting domains or modules, as well as the mutation

of individual domains to alter their specificity (Hahn & Stachelhaus, 2006). Although some of

the domain swapping experiments have been successful in the production of altered products,

a major stumbling block has been the fact that most of the chimeric NRPSs were functionally

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1865499/#R20


46

impaired and produced small amounts of the product (Giessen & Marahiel, 2012). However,

the identification of linker regions that bridge the individual modules within an NRPS and a

better understanding of the domain borders has allowed these approaches to remain viable. The

linker regions are about 15 amino acids in length and do not contain conserved residues. The

fact that these linker regions are able to connect individual modules, in the absence of any

conserved residues, has made them the ideal candidate for artificial module fusions. Indeed,

in vivo biochemical studies on the tyrocidin synthetase showed that the fusion of modules

within the linker regions resulted in the production of satisfying amounts of the altered peptide

product (Schwarzer et al., 2003).

Furthermore, the elucidation of the molecular basis for the selective interaction between NRPS

modules via communication-mediating (COM) domains has also widened the toolbox for the

combinatorial manipulation of NRPSs (Hahn & Stachelhaus, 2006). According to a study by

Hahn & Stachelhaus (2004), a donor COM domain located at the C terminus of an aminoacyl-

or peptidyl-donating NRPS and an acceptor COM domain located at the N terminus of the

accepting cognate NRPS form a compatible set, which facilitates the intermolecular

communication between adjacent modules. Recognition between the donor and acceptor

domains are mediated by electrostatic and/or polar interactions between five pairs of residues

located in both of the compatible COM domains. Additional studies have revealed that the

swapping of COM domains can be used to manipulate the interaction of enzymes within the

NRPS complex leading to the simultaneous production of different peptide products (Hahn &

Stachelhaus, 2006).

The recombination of whole modules does represent a rather drastic intervention in the

biosynthesis of NRPS-produced compounds, but eventually these approaches may lead to the

combinatorial biosynthesis of innovative peptide antibiotics. Combinatorial biosynthesis has

the potential to be a powerful way to generate antibiotic derivatives with greater antibacterial

activity and/or improved pharmacokinetic properties. It has advantages over the chemical

derivatisation of antibiotic molecules, since the bacterial biosynthetic enzymes carry out

site-specific and enantiomer-specific reactions, by-passing the need to protect reactive

functional groups in each reaction step in the chemical approach. This ensures that only the

desired product is produced, which enhances the product yield.


47

1.5 RESEARCH AIMS

The actinomycete, Streptomyces polyantibioticus SPRT, was isolated from soil collected from

the banks of the Umgeni River, KwaZulu-Natal Province, South Africa, as part of an antibiotic-

screening programme (Le Roes-Hill & Meyers, 2009). It exhibits antibiosis against various

Gram-positive and Gram-negative bacteria, including Enterococcus faecium VanA (a

vancomycin-resistant strain), Mycobacterium aurum A+ (which has a similar antibiotic

susceptibility to M. tuberculosis, but is not pathogenic; Chung et al., 1995) and E. coli ATCC

25922 (Le Roes, 2005). Of great interest, however, was its antibiotic activity against M.

tuberculosis H37RvT, which prompted interest in its antibiotic production.

An antibacterial compound produced by S. polyantibioticus SPRT was isolated and its structure

was determined by X-ray crystallography and nuclear magnetic resonance (NMR) to be 2,5-

diphenyloxazole (DPO; Figure 1.20) (Le Roes, 2005). An independent report by Giddens et

al. (2005) confirmed that DPO (produced by chemical synthesis) showed activity against non-

replicating persistent cells of M. tuberculosis, which are difficult to eradicate using traditional

anti-TB drugs. The authors suggested that simple oxazole derivatives such as DPO may

therefore be feasible options in the search for new antitubercular agents. DPO is currently only

known to be synthesised chemically (Adrova et al., 1956), therefore its discovery from a

biological origin is of great interest. DPO is unusual in that it is a 2,5-disubstituted oxazole,

whereas most other disubstituted oxazoles from biological sources are 2,4-substituted.

Based on the structure of DPO, a biosynthetic scheme for the synthesis of this molecule was

proposed, whereby a NRPS condenses a molecule of benzoic acid with 3-

hydroxyphenylalanine. The resulting benzoyl-β-hydroxyphenylalanine is converted to DPO

by heterocyclisation, oxidation and decarboxylation.

It seems likely that DPO is synthesized non-ribosomally by S. polyantibioticus SPRT due to the

presence of an oxazole. The NRPS responsible for the biosynthesis of DPO is proposed to have

an A domain specific for the activation of phenylalanine or 3-hydroxyphenylalanine, plus

ArCP, Cy, Ox, PCP and TE domains.


48

Figure 1.20 The structure of 2,5-diphenyloxazole (DPO).

The overall aim of this study was to confirm the production of DPO by S. polyantibioticus

SPRT and then to focus on the elucidation of the biosynthetic pathway involved in its synthesis.

This consisted of the identification and partial characterization of the genes involved in the

production of DPO to establish whether an NRPS is involved.

In order to determine whether the proposed biosynthetic pathway is correct, the genes coding

for benzoic acid synthesis and the DPO NRPS had to be identified in the S. polyantibioticus

SPRT genome. The aims of the study were thus:

(i) To identify the genes involved in joining benzoic acid and phenylalanine/3-

hydroxyphenylalanine in S. polyantibioticus SPRT to create a 2,5-disubstituted oxazole.

(ii) To identify the genes responsible for the biosynthesis of benzoic acid in S. polyantibioticus

SPRT.

(iii) To propose a pathway for the biosynthesis of DPO in S. polyantibioticus SPRT.

(iv) To develop a method to introduce recombinant plasmids into S. polyantibioticus SPRT.


49

(v) To prove the involvement of genes in DPO biosynthesis through the creation of selected

gene knockouts in S. polyantibioticus SPRT.

Lastly, the genetic information from S. polyantibioticus SPRT will help to lay the foundation

for future combinatorial biosynthetic studies, using the genes responsible for DPO production

to develop a range of oxazole derivatives that could be tested for enhanced antitubercular

activity and therefore could become candidates for development as novel drugs to treat drug-

resistant tuberculosis.


50

1.6 REFERENCE LIST Adrova, N.A., Koton, M.M. & Florinsky, F.S. (1956). Preparation of 2,5-Diphenylaoxazole and its Scintillation Efficiency in Plastics. Institute of Macromolecular Compounds of the Academy of Sciences of the USSR, 63(3): 394-395. Ansari, M.Z., Yadav, G., Gokhale, R.S. & Mohanty, D. (2004). NRPS-PKS: a knowledge-based resource for analysis of NRPS/PKS megasynthases. Nucleic Acids Research, 32: 405-413. Applebaum, P.C. (2006). The emergence of vancomycin-intermediate and vancomycin-resistant Staphylococcus aureus. Clinical Microbiology and Infection, 12(1):16-23. Ashforth, E. J., Fu, C., Liu, X., Dai, H., Song, F., Guo, H. & Zhang, L. (2010). Bioprospecting for antituberculosis leads from microbial metabolites, Natural Product Reports. 27: 1709–1719. Bachmann, B.O. & Ravel, J. (2009). Chapter 8. Methods for in silico prediction of microbial polyketide and nonribosomal peptide biosynthetic pathways from DNA sequence data. Methods in Enzymology, 458: 181-217. Balibar, C.J., Vaillancourt, F.H. & Walsh, C.T. (2005). Generation of D amino acid residues in assembly of arthrofactin by dual condensation/epimerization domains. Chemistry & Biology, 12(11): 1189-1200 Baltz, R.H. (2008). Renaissance in antibacterial discovery from actinomycetes. Current Opinion in Pharmacology, 8:557–563

Baltz, R.H. (2014). MbtH homology codes to identify gifted microbes for genome mining. Journal of Industrial Microbiology and Biotechnology, 41(2): 357-69. Baranasic, D., Zucko, J., Diminic, J., Gacesa, R., Long, P.F., Cullum, J., Hranueli, D. & Starcevic, A. (2013). Predicting substrate specificity of adenylation domains of nonribosomal peptide synthetases and other protein properties by latent semantic indexing. Journal of industrial microbiology & biotechnology, 41(2): 461-467. Barry, C. E. 3rd, Boshoff, H. I., Dartois, V., Dick, T., Ehrt, S., Flynn, J., Schnappinger, D., Wilkinson, R. J. & Young, D. (2009). The spectrum of latent tuberculosis: rethinking the biology and intervention strategies Nature Reviews Microbiology, 7: 845-855. Bentley, S.D., Chater, K.F., Cerdeño-Tárraga, A.M., Challis, G.L., Thomson, N.R., James, K.D., Harris, E., Quail, M., A., Kieser, H., Harper, D., Bateman, A., Brown, S., Chandra, G., Chen, C.W., Collins, M., Cronin, A., Fraser, A., Goble, A., Hidalgo, J., Hornsby, T., Howarth, S., Huang, C.H., Kieser, T., Larke, L., Murphy, L., Oliver, K., O'Neil, S., Rabbinowitsch, E., Rajandream, M.A., Rutherford, K., Rutter, S., Seeger, K., Saunders, D., Sharp, S., Squares, R., Squares, S., Taylor, K., Warren, T., Wietzorrek, A., Woodward, J., Barrell, B.G., Parkhill, J. & Hopwood, D.A. (2002). Complete genome sequence of the model actinomycete Streptomyces coelicolor A3(2). Nature, 417: 141-147. Bérdy, J. (2005). Bioactive microbial metabolites. The Journal of Antibiotics, 58: 1-26. Bhate, D. S., Hulyalkar, R. K. & Menon, S. K. (1960). Isolation of iso-butyropyrrothine along with thiolutin and aureothricin from a Streptomyces sp. Experientia, 16: 504. Bloom, B.R. & Murray, C.J.L. (1992). Tuberculosis: commentary on a re-emergent killer. Science, 257: 1055-1064.

http://www.ncbi.nlm.nih.gov/pubmed/24197465



51

Bloudoff, K., Rodionov, D. & Schmeing, T.M. (2013). Crystal Structures of the First Condensation Domain of CDA Synthetase Suggest Conformational Changes during the Synthetic Cycle of Nonribosomal Peptide Synthetases. Journal of Molecular Biology, 425: 3137-3150. Cane, D.E., Walsh, C.T. & Khosla, C. (1998). Harnessing the biosynthetic code: Combinations, permutations and mutations. Science, 282: 63-68. Cane, D.E. & Walsh, C.T. (1999). The parallel and convergent universe of polyketide synthases and nonribosomal peptide synthetases. Chemistry & Biology, 6(12): 319-325. Cape Gateway, Department of Health (Provincial Government of the Western Cape). (2006). Last accessed January 2015. http://www.capegateway.gov.za/eng/pubs/public_info/M/115549. Centers for Disease Control and Prevention (CDC). (2013). Last accessed January 2015. http://www.cdc.gov/drugresistance/threat-report-2013/. Challis, G.L. & Ravel, J. (2000). Coelichelin, a new peptide siderophore encoded by the Streptomyces coelicolor genome: structure prediction from the sequence of its non-ribosomal peptide synthetase. FEMS Microbiology Letters, 187: 111-114. Challis, G.L., Ravel, J. & Townsend, C.A. (2000). Predictive, structure-based model of amino acid recognition by nonribosomal peptide synthetase adenylation domains. Chemistry & Biology, 7(3): 211-224. Challis, G.L. (2014). Exploitation of the Streptomyces coelicolor A3(2) genome sequence for discovery of new natural products and biosynthetic pathways. Journal of Industrial Microbiology and Biotechnology, 41: 219–232. Chater, K.F. (1990). The Improving Prospects for Yield Increase by Genetic Engineering in Antibiotic-Producing Streptomycetes. Nature Biotechnology. 8: 115 – 121. Chung, G.A. C., Aktar, Z., Jackson, S. & Duncan, K. (1995). High-throughput screen for detecting antimycobacterial agents. Antimicrobial Agents and Chemotherapy, 39: 2235-2238. Churchyard, G.J., Mametja, L.D., Mvusi, L., Ndjeka, N., Hesseling, A.C., Reid, A., Babatunde, S. & Pillay, Y. (2014). Tuberculosis control in South Africa: Successes, challenges and recommendations. South African Medical Journal, 104(3): 244-248. Condurso, H.L. & Bruner, S.D. (2012). Structure and noncanonical chemistry of nonribosomal peptide biosynthetic machinery. Natural Product Reports, 29(10): 1099-1110. Conti, E., Stachelhaus, T., Marahiel, M.A. & Brick, P. (1997). Structural basis for the activation of phenylalanine in the non-ribosomal biosynthesis of gramicidin S. The EMBO Journal, 16(14): 4174-4183. Cragg, G.M. & Newman, D.J. (2013). Natural products: A continuing source of novel drug leads. Biochimica et Biophysica Acta, 1830(6): 3670–3695. Crawford, J.M., Portmann, C., Kontnik, R., Walsh, C.T. & Clardy, J. (2011). NRPS substrate promiscuity diversifies the Xenematides. Organic Letters, 13(19): 5145-5147. Dantas, G. & Sommer, M.O.A. (2014). How to Fight Back Against Antibiotic Resistance. American Scientist, 102: 42-51

http://www.capegateway.gov.za/eng/pubs/public_info/M/115549

http://www.cdc.gov/drugresistance/threat-report-2013/


52

Davies, J. (2007). Microbes have the last word. European Molecular Biology Organization Reports, 8(7): 616-621. Davies, J. (2011). How to discover new antibiotics: harvesting the parvome. Current Opinion in Chemical Biology, 15: 5–10. Davies, J. (2012). Antibiotic discovery: then and now. Microbiology Today, 39(4): 200-203. Davies, J. & Ryan, K.S. (2012). Introducing the Parvome: Bioactive Compounds in the Microbial World. ACS Chemical Biology, 7: 252−259 Demain, A.L. & Sanchez, S. (2009). Microbial drug discovery: 80 years of progress. The Journal of Antibiotics, 62: 5–16. Du, L., Chen, M., Sanchez, C. & Shen, B. (2000). An oxidation domain in the BlmIII non-ribosomal peptide synthetase probably catlyzing thiazole formation in the biosynthesis of the anti-tumor drug bleomycin in Streptomyces verticillus ATCC15003. FEMS Microbiology Letters, 189: 171-175. Duerfahrt, T., Eppelmann, K., Müller, R., & Marahiel, M.A. (2004). Rational Design of a Bimodular Model System for the Investigation of Heterocyclization in Nonribosomal Peptide Biosynthesis. Chemistry & Biology, 11: 261–271. Felnagle, E.A., Jackson, E.E., Chan, Y.A., Podevels, A.M., Berti, A.D., McMahon, M.D. & Thomas, M.G. (2008). Nonribosomal peptide synthetases involved in the production of medically relevant natural products. Molecular Pharmaceutics, 5(2): 191-211. Finking, R. & Marahiel, M.A. (2004). Biosynthesis of nonribosomal peptides. Annual Review of Microbiology, 58: 453-488. Fischbach, M.A. & Walsh, C.T. (2006). Assembly-line enzymology for polyketide and nonribosomal peptide antibiotics: logic, machinery and mechanisms. Chemical Reviews, 106: 3468-3496. Fischbach, M.A. & Walsh, C.T. (2009). Antibiotics For Emerging Pathogens. Science, 325: 1089-1093. Floss, H.G. (2006). Combinatorial Biosynthesis – Potential and Problems. Journal of Biotechnology, 124(1): 242–257. Fusetani, N., Sugawara, T. & Matsunaga, S. (1991). Orbiculamide A: A novel cytotoxic cyclic peptide from a marine sponge Theonella sp. Journal of The American Chemical Society, 113: 7812-7813. Gaitatzis, N., Kunze, B. & Muller, R. (2001). In vitro reconstitution of the myxochelin biosynthetic machinery of the Stigmatella aurantiaca Sg a15: Biochemical characterization of a reductive release meachansim from nonribosomal peptide synthetases. Proceedings of the National Academy of Sciences of the USA, 98(20): 11136-11141. Galm, U., Wang, W., Wendt-Pienkowski, E., Yang, R., Liu, W., Tao, M., Coughlin, J.,M., Shen, B. (2008). In Vivo Manipulation of the Bleomycin Biosynthetic Gene Cluster in Streptomyces verticillus ATCC15003 Revealing New Insights into Its Biosynthetic Pathway. The Journal of Biological Chemistry, 283(42): 28236-28245. Gehring, A.M. & Walsh C.J. (1998). Iron acquisition in the plague: modular logic in enzymatic biogenesis of yersiniabactin by Yersinia pestis. Chemistry & Biology, 5: 573-586.

http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=16414140

http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=16414140


53

GenBank. (2015). Last accessed 13 July 2015. http://www.ncbi.nlm.nih.gov/genome/browse/. Giddens, A.C., Boshoff, H.I.M., Franzblau, S.G., Barry III, C.E. & Copp, B.R. (2005). Antimycobacterial natural products: synthesis and preliminary biological evaluation of the oxazole-containing alkaloid texaline. Tetrahedron letters, 46(43): 7355-7357 Giessen, T.W. & Marahiel, M.A. (2012). Ribosome-independent biosynthesis of biologically active peptides: Application of synthetic biology to generate structural diversity. FEBS Letters, 586: 2065-2075. Gocht, M. & Marahiel, M.A. (1994). Analysis of core sequences in the D-Phe activating domain of the multifunctional peptide synthetase TycA by site directed mutagenesis. Journal of Bacteriology, 176: 2654-2662. Hahn, M. & Stachelhaus, T. (2004). Selective interaction between nonribosomal peptide synthetases is facilitated by short communication-mediating domains. Proceedings of the National Academy of Sciences of the USA, 101: 15585-15590. Hahn, M. & Stachelhaus, T. (2006). Harnessing the potential of communication-mediating domains for the biocombinatorial synthesis of nonribosomal peptides. Proceedings of the National Academy of Sciences of the USA, 103: 275-280. Handelsman, J., Rondon, M.R., Brady, S.F., Clardy, J., Goodman, R.M. (1998). Molecular biological access to the chemistry of unknown soil microbes: a new frontier for natural products. Chemistry & Biology, 5(10): 245-249. Harvey, A. (2000). Strategies for discovering drugs from previously unexplored natural products. Drug Discovery Today, 5(7): 294-300. Hopwood D.A., Malpartida, F., Kieser, H.M., Ikeda, H., Duncan, J., Fujii, I., Rudd, B.A.M., Floss, H.G. & Omura, S. (1985). Production of “hybrid” antibiotics by genetic engineering. Nature, 314: 642–644. Howden, B.P., Davies, J.K., Johnson, P.D.R., Stinear, T.P. & Grayson, M.L. (2010). Reduced Vancomycin Susceptibility in Staphylococcus aureus, including Vancomycin-Intermediate and Heterogeneous Vancomycin-Intermediate Strains: Resistance Mechanisms, Laboratory Detection, and Clinical Implications. Clinical Microbiology Reviews, 23(1): 99–139. Hugenholtz, P., Goebel, B.M. & Pace, N.R. (1998). Impact of Culture-Independent Studies on the Emerging Phylogenetic View of Bacterial Diversity. Journal of Bacteriology, 180(18): 4765-4774. Inahashi, Y., Iwatsuki, M., Ishiyama, A., Namatame, M., Nishihara-Tsukashima, A., Matsumoto, A., Hirose, T., Sunazuka, T., Yamada, H., Otoguro, K., Takahashi, Y., Omura, S. & Shiomi, K. (2011). Spoxazomicins A-C, novel antitrypanosomal alkaloids produced by an endophytic actinomycete, Streptosporangium oxazolinicum K07-0460(T). Journal of Antibiotics (Tokyo), 64(4): 303-307. Jackman, J.E., Fierke, C.A., Tumey, L.N., Pirrung, M., Uchiyama, T., Tahir, S.H., Hindsgaul, O. & Raetz, C.R. (2000). Antibacterial agents that target lipid A biosynthesis in gram-negative bacteria. Inhibition of diverse UDP-3-O-(r-3-hydroxymyristoyl)-n-acetylglucosamine deacetylases by substrate analogs containing zinc binding motifs. Journal of Biological Chemistry, 275(15): 11002-11009. John, J.E. (2009). Natural products-based drug discovery: some bottlenecks and considerations. Current Science, 96(6): 753.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=22273582do

http://www.ncbi.nlm.nih.gov/pubmed/?term=Howden%20BP%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Davies%20JK%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Johnson%20PD%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Stinear%20TP%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Grayson%20ML%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Jackman%20JE%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Fierke%20CA%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Tumey%20LN%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Pirrung%20M%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Uchiyama%20T%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Tahir%20SH%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Hindsgaul%20O%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Raetz%20CR%5BAuthor%5D&cauthor=true&cauthor_uid=10753902

http://www.ncbi.nlm.nih.gov/pubmed/?term=Raetz%20CR%5BAuthor%5D&cauthor=true&cauthor_uid=10753902


54

Keating, T.A. & Walsh, C.T. (1999). Initiation, elongation and termination strategies in polyketide and polypeptide antibiotic biosynthesis. Current Opinion in Chemical Biology, 3: 598-606. Keating, T.A., Marshall, C.G., Walsh, C.T. & Keating, A.E. (2002). The structure of VibH represents nonribosomal peptide synthetase condensation, cyclization and epimerization domains. Nature Structural Biology, 9: 522-6. Khurana, P., Gokhale, R.S. & Mohanty, D. (2010). Genome scale prediction of substrate specificity for acyl adenylate superfamily of enzymes based on active site residue profiles. BMC Bioinformatics, 11: 57. Kleinkauf, H. & von Döhren, H. (1990). Nonribosomal biosynthesis of peptide antibiotics. European Journal of Biochemistry, 192(1): 1–15. Kobayashi, J., Itagaki, F., Shigemori, I., Takao, T. & Shimonishi, Y. (1995). Keramamides E, G, H, and J, new cyclic peptides containing an oxazole or a thiazole ring from a Theonella sponge. Tetrahedron, 51(9): 2525-2532. Kondo, K., Higuchi, Y., Sakuda, S., Nihira, T. & Yamada, Y. (1989). New virginiae butanolides from Streptomyces virginiae. The Journal of antibiotics, 42(12): 1873-1876. Konz, D., Klens, A., Schbrgendorfer, K., Marahiel, M.A. (1997). The bacitracin biosynthesis operon of Bacillus licheniformis ATCC 10716: molecular characterization of three multi-modular peptide synthetases. Chemistry & Biology, 4: 927-937. Konz, D. & Marahiel, M.A., (1999). How do peptide synthetases generate structural diversity? Chemistry & Biology, 6(2): 39-48. Kopp, F. & Marahiel, M.A. (2007). Macrocyclization Strategies in Polyketide and Nonribosomal Peptide Biosynthesis. Natural Product Reports, 24(4): 735-749. Koul, A., Arnoult, E., Lounis, N., Guillemont, J. & Andries, K. (2011). The challenge of new drug discovery for tuberculosis. Nature, 469: 483-490. Lambalot, R.H., Gehring, A.M., Flugel, R.S., Zuber, P., LaCelle, M., Marahiel, M.A., Reid, R., Khosla, C. & Walsh, C.T. (1996). A new enzyme superfamily – the phosphopantetheinyl transferases. Chemistry & Biology, 3: 923-936. Lamichhane, G. (2011). Novel targets in M. tuberculosis: search for new drugs. Trends in Molecular Medicine, 17(1): 25-33. Land, M., Hauser, L., Jun, S., Nookaew, I., Leuze, M.R., Ahn, T., Karpinets, T., Lund, O., Kora, G., Waasenaar, T., Poudel, S. & Ussery, D.W. (2015). Insights from 20 years of bacterial genome sequencing. Functional & Integrative Genomics, DOI 10.1007/s10142-015-0433-4. Lautru, S. & Challis, G.L. (2004). Substrate recognition by nonribosomal peptide synthetase multi-enzymes. Microbiology, 150: 1629-1636. Lautru, S., Deeth, R.J., Bailey, L.M., Challis, G.L. (2005). Discovery of a new peptide natural product by Streptomyces coelicolor genome mining. Nature Chemical Biology, 1: 265-269.


55

Le Roes, M. (2005). Selective isolation characterization and screening of actinomycetes for novel anti-tubercular antibiotics. PhD Thesis, Department of Molecular and Cell Biology, University of Cape Town. Chapter 5, 167-182. Le Roes-Hill, M. & Meyers, P. R. (2009). Streptomyces polyantibioticus sp. nov., isolated from the banks of a river. International Journal of Systematic and Evolutionary Microbiology, 59: 1302–1309. Li, J. & Jensen, S.E. (2008). Nonribosomal biosynthesis of fusaricidins by Paenibacillis polymyxa PKB1 involves direct activation of a D-amino acid. Chemistry & Biology, 15(2): 118-127. Li, J.W. & Vederas, J.C. (2009). Drug discovery and natural products: end of an era or an endless frontier? Science, 325(5937): 161-165. Li, M.H.T., Ung, P.M.U., Zajkowski, J., Garneau-Tsodikova, S. & Sherman, D.H. (2009). Automated genome mining for natural products. BMC Bioinformatics, 10: 185. Liu, X., Chen, C., He, W., Huang, P., Liu, M., Wang, Q., Guo, H., Bolla, K., Lu, Y., Song, F., Dai, H., Liu, M. & Zhang, L. (2012). Exploring anti-TB leads from natural products library originated from marine microbes and medicinal plants. Antonie van Leeuwenhoek, 102: 447-461. MacNeil, D., J., Gewain, K., M., Ruby, C., L., Dezeny, G., Gibbons, P., H. & MacNeil, T. (1992). Analysis of Streptomyces avermitilis genes required for avermectin biosynthesis utilizing a novel integration vector. Gene, 111(1): 61. Marahiel, M.A. (1997). Protein templates for the biosynthesis of peptide antibiotics. Chemistry & Biology, 4(8): 561-567. Marahiel, M.A. (2009). Working outside the protein-synthesis rules: insights into non-ribosomal protein synthesis. Journal of Peptide Science, 15: 799-807. May, J.J., Kessler, N., Marahiel, M.A. & Stubbs, M.T. (2002). Crystal structure of DhbE, an archetype for aryl acid activating domains of nonribosomal peptide synthetases. Proceedings of the National Academy of Science of the USA, 99(19): 12120-12125. Miao, V. & Davies, J. (2010). Actinobacteria: the good, the bad, and the ugly. Antonie van Leeuwenhoek, 98: 143–150. Michels, P.C., Khmelnitsky, Y.L., Dordick, J.S. & Clark, D.S. (1998). Combinatorial biocatalysis: a natural approach to drug discovery. Trends in Biotechnology, 16(5): 210-215. Milne, J.C., Eliot, A.C., Kellher, N.L. & Walsh, C.T. (1998). ATP/GTP hydrolysis is required for oxazole and thiazole biosynthesis in the peptide antibiotic microcin B17. Biochemistry, 37(38): 13250-13261. Mootz, H.D., Schwarzer, D. & Marahiel, M.A. (2002). Ways of assembling complex natural products on modular nonribosomal peptide synthetases. ChemBioChem, 3: 490-504. Nett, M., Ikedab, H. & Moore, B., S. (2009). Genomic basis for natural product biosynthetic diversity in the actinomycetes. Natural Product Reports, 26: 1362–1384. Padmavathi, V., Mahesh, K., Rangayapalle, D., Venkata, C., Deepti, D. & Reddy, G.S. (2009). Synthesis and biological activity of a new class of sulfone linked bis(heterocycles). Arkivoc, 2: 195-208.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Michels%20PC%5BAuthor%5D&cauthor=true&cauthor_uid=9621460

http://www.ncbi.nlm.nih.gov/pubmed/?term=Khmelnitsky%20YL%5BAuthor%5D&cauthor=true&cauthor_uid=9621460

http://www.ncbi.nlm.nih.gov/pubmed/?term=Dordick%20JS%5BAuthor%5D&cauthor=true&cauthor_uid=9621460

http://www.ncbi.nlm.nih.gov/pubmed/?term=Clark%20DS%5BAuthor%5D&cauthor=true&cauthor_uid=9621460


56

Pavela-Vrancic, M., van Liempt, H., Pfeifer, E., Freist, W. & von Dohren, H. (1994). Nucleotide binding by multienzyme peptide synthetases. European Journal of Biochemistry, 220(2): 535-542. Petrini, B. & Hoffner, S. (1999). Drug-resistant and multidrug-resistant tubercle bacilli. International Journal of Antimicrobial Agents, 13: 93-97. Prieto, C., Garcia-Estrada, C., Lorenzana, D. & Martin, J.F. (2012). NRPSsp: non-ribosomal peptide synthase substrate predictor. Bioinformatics, 28(3): 426-427. Pulsawat, N., Kitani, S. & Nihira, T. (2007). Characterization of biosynthetic gene cluster for the production of virginiamycin M, a streptogramin type A antibiotic, in Streptomyces virginiae. Gene, 393: 31-42. Qiao, C., Wilson, D.J., Bennett, E.M. & Aldrich, C.C. (2007). A mechanism-based aryl carrier protein/thiolation domain affinity probe. Journal of the American Chemical Society, 129: 6350-6351. Rastogi, N., Abaul, J., Goh, K.S., Devallois, A., Philogene, E. & Bourgeois, P. (1998). Antimycobacterial activity of chemically defined natural substances from the Caribbean flora in Guadeloupe. FEMS Immunology and Medical Microbiology, 20(4): 267-273. Rausch, C. Weber, T., Kohlbacher, O., Wohlleben, W. & Huson, D.H. (2005). Specificity prediction of adenylation domains in nonribosomal peptide synthetases (NRPS) using transductive support vector machines (TSVMs). Nucleic Acids Research, 33: 5799-808.

Reynolds, K. A. (1998). Combinatorial biosynthesis: lesson learned from nature. Proceedings of the National Academy of Sciences of the USA, 95: 12744-12746.

Röttig, M., Medema, M.H., Blin, K., Weber, T., Rausch, C. & Kohlbacher, O. (2011). NRPSpredictor2 – a web server for predicting NRPS adenylation domain specificity. Nucleic Acids Research, 1-6.

Roy, R.S., Gehring, A.M., Milne, J.C., Belshaw, P.J. & Walsh, C.T. (1999). Thiazole and oxazole peptides: biosynthesis and molecular machinery. Natural Product Reports, 16: 249 – 263.

Rivers, E. C. & Mancera, R. L. (2008). New anti-tuberculosis drugs in clinical trials with novel mechanisms of action. Drug Discovery Today, 13: 1090-1098. Samel, S.A., Schoenafinger, G., Knappe, T.A., Marahiel, M.A. & Essen, L. (2007). Structural and Functional Insights into a Peptide Bond-Forming Bidomain from a Nonribosomal Peptide Synthetase. Structure, 15: 781–792. Schmoock, G., Pfennig, F., Jewiarz, J., Schlumbohm, W., Laubinger, W., Schauwecker, F. & Keller, U. (2005). Functional Cross-talk between Fatty Acid Synthesis and Nonribosomal Peptide Synthesis in Quinoxaline Antibiotic-producing Streptomycetes. The Journal of Biological Chemistry, 280(6): 4339-4349. Schwarzer, D., Finking, R. & Marahiel, M.A. (2003). Nonribosomal peptides: from genes to products. Natural Product Reports, 20: 275-287. Seow, K.T., Meurer, G., Gerlitz, M., Wendt-Pienkowski, E., Hutchinson, C.R. & Davies, J. (1997). A study of iterative type II polyketide synthases, using bacterial genes cloned from soil DNA: a means to access and use genes from uncultured microorganisms. Journal of Bacteriology, 179(23): 7360-7368. Sieber, S.A. & Marahiel, M.A. (2005). Molecular mechanisms underlying nonribosomal peptide synthesis: approaches to new antibiotics. Chemical Reviews, 105: 715-738.


57

Spratt, B.G. (1994). Resistance to antibiotics mediated by target alterations. Science, 264: 388. Stachelhaus, T., Hüser, A. & Marahiel, M.A. (1996). Biochemical characterization of peptidyl carrier protein (PCP), the thiolation domain of multifunctional peptide synthetases. Chemistry & Biology, 3: 913-921. Stachelhaus, T., Mootz, H.D, & Marahiel, M.A. (1999). The specificity-conferring code of adenylation domains in nonribosomal peptide synthetases. Chemistry & Biology, 6: 493-505. Strieker, M., Tanović, A. & Marahiel, M.A. (2010). Nonribosomal peptide synthetases: structures and dynamics. Current Opinion in Structural Biology, 20: 234-240. Subramani, R. & Aalbersberg, W. (2013). Culturable rare Actinomycetes: diversity, isolation and marine natural product discovery. Applied Microbiology & Biotechnology, 97: 9291-9321. Suo, Z., Tseng, S.A. & Walsh, C.T. (2001). Purification, priming, and catalytic acylation of carrier protein domains in the polyketide synthase and nonribosomal peptidyl synthetase modules of the HMWP1 subunit of yersiniabactin synthetase. Proceedings of the National Academy of Science of the USA, 95(1): 99-104. Tanovic, A. Samel, S.A., Essen, L.O. & Marahiel, M.A. (2008). Crystal structure of the termination module of a nonribosomal peptide synthetase. Science, 321: 659-63. Tao, M., Wang, L., Wendt-Pienkowski, E., George, N.P., Galm, U., Zhang, G., Coughlin, J.M. & Shen, B. (2007). The tallysomycin biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 unveiling new insights into the biosynthesis of the bleomycin family of antitumor antibiotics. Molecular Biosystems, 3(1): 60-74. Udwadia, Z., F. (2012). MDR, XDR, TDR tuberculosis: ominous progression. Thorax, 67(4): 286-288. Udwadia Z., F., Vendoti, D. (2013). Totally drug-resistant tuberculosis (TDR-TB) in India: every dark cloud has a silver lining. Journal of Epidemiology and Community Health. 67(6): 471-472. Ullrich, M. & Bender, C.L. (1994). The biosynthetic gene cluster for coronamic acid, an ethylcyclopropyl amino acid, contains genes homologous to amino acid-activating enzymes and thioesterases. Journal of Bacteriology, 176: 7574-7586. Van Lanen, S. & Shen, B. (2006). Microbial genomics for the improvement of natural product discovery. Current Opinion in Microbiology, 9: 252-262. Velasco, A., Acebo, P., Gomez, A., Schleissner, C., Rodriguez, P., Aparicio, T., Conde, S., Munoz, R., de la Calle, F., Garcia, J.L. & Sanchez-Puelles, J.M. (2005). Molecular characterization of the safracin biosynthetic pathway from Pseudomonas fluorescens A2-2: designing new cytotoxic compounds. Molecular Microbiology, 56(1): 144-154. Ventura, M., Canchaya, C., Tauch, A., Chandra, G., Fitzgerald, G., F., Chater, K., F. & van Sinderen, D. (2007). Genomics of Actinobacteria: Tracing the Evolutionary History of an Ancient Phylum. Microbiology and Molecular Biology Reviews. 71(3): 495–548. Verma, M., Lal, D., Kaur, J., Saxena, A., Kaur, J., Anand, S. & Lal, R. (2013). Phylogenetic analyses of phylum Actinobacteria based on whole genome sequences. Research in Microbiology. 164: 718-728. Von Döhren, H., Dieckmann, R. & Pavela-Vrancic, M. (1999). The nonribosomal code. Chemistry & Review, 6(10): 273-279.


58

Waksman, S.A. (1947). What Is an Antibiotic or an Antibiotic Substance? Mycologia, 39: 565-569. Walsh, C.T. Chen, H., Keating, T.A., Hubbard, B.K., Losey, H.C., Luo, L., Marshall, C.G., Miller, D.A., & Patel, H.M. (2001). Tailoring enzymes that modify nonribosomal peptides during and after chain elongation on NRPS assembly lines. Current Opinion in Chemical Biology, 5: 525-534. Walsh, C.T. (2004). Polyketide and nonribosomal peptide antibiotics: modularity and versatility. Science, 303: 1805-1810. Walsh, C.T. & Fischbach, M.A. (2010). Natural Products Version 2.0: Connecting Genes to Molecules. Journal of the American Chemical Society, 132(8): 2469-2493. Wang, L., Yun, B., George, N.P., Wendt-Pienkowski, E., Galm, U., Oh, T., Coughlin, J.M., Zhang, G., Tao, M. & Shen, B. (2007). The Glycopeptide Antitumor Antibiotic Zorbamycin from Streptomyces flavoviridis ATCC 21892: Strain Improvement and Structure Elucidation. Journal of Natural Products, 70(3): 402-406. Watve, M.G., Tickoo, R., Jog, M.M., Bhole, B.D. (2001). How many antibiotics are produced by the genus Streptomyces? Archives of microbiology, 176(5): 386-90. Weber, T., Blin, K., Duddela, S., Krug, D., Kim, H.U., Bruccoleri, R., Lee, S.Y., Fischbacj, M.A., Muller, R., Wohlleben, W., Breitling, R., Takano, E., & Medema, M.H. (2015). antiSMASH 3.0 — a comprehensive resource for the genome mining of biosynthetic gene clusters. Nucleic Acids Research, doi: 10.1093/nar/gkv437 Weissman, K. J. & Leadlay, P. F. (2005). Combinatorial biosynthesis of reduced polyketides. Nature Reviews: Microbiology; 3: 925-936. World Health Organisation (WHO). (2014). Last accessed 12 January 2015. http://www.who.int/mediacentre/factsheets/fs104/en/. Wu, D., Hugenholtz. P., Mavromatis, K., Pukall, R., Dalin, E., Ivanova, N. N., Kunin, V., Goodwin, L., Wu, M., Tindall, B. J., Hooper, S. D., Pati, A., Lykidis, A., Spring, S., Anderson, I.J., D'haeseleer, P., Zemla, A., Singer, M., Lapidus, A., Nolan, M., Copeland, A., Han, C., Chen, F., Cheng, J.F., Lucas, S., Kerfeld, C., Lang, E., Gronow, S., Chain, P., Bruce, D., Rubin, E.M., Kyrpides, N.C., Klenk, H.P. & Eisen, J.A. (2009). A phylogeny-driven genomic encyclopaedia of Bacteria and Archaea. Nature; 462: 1056-1060. Xia, S., Ma, Y., Zhang, W., Yang, Y., Wu, S., Zhu, M., Deng, L., Li, B., Liu, Z. & Qi, C. (2012). Identification of Sare0718 as an alanine-activating adenylation domain in marine actinomycete Salinispora arenicola CNS-205. PLoS One, 7(5): 1-12. Yeh, V.S.C. (2004). Recent advances in the total synthesis of oxazole-containing natural products. Tetrahedron 60: 11995 – 12042. Yoshioka, T., Mohri, K., Oikawa, Y. & Yonemitsu, 0. (1981). Metabolism of Streptoverticilium olivoreticuli and Streptomyces cinnamomeus. Journal of Chemical Research, 194. Young, D. B., Gideon, H. P. & Wilkinson, R. J. (2009). Eliminating latent tuberculosis. Trends in Microbiology, 17: 183-188.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Tickoo%20R%5BAuthor%5D&cauthor=true&cauthor_uid=11702082

http://www.ncbi.nlm.nih.gov/pubmed/?term=Jog%20MM%5BAuthor%5D&cauthor=true&cauthor_uid=11702082

http://www.ncbi.nlm.nih.gov/pubmed/?term=Bhole%20BD%5BAuthor%5D&cauthor=true&cauthor_uid=11702082

http://www.who.int/mediacentre/factsheets/fs104/en/

59

CHAPTER 2

EARLY ATTEMPTS AT ISOLATING THE GENE CLUSTER

RESPONSIBLE FOR DPO BIOSYNTHESIS IN STREPTOMYCES

POLYANTIBIOTICUS SPRT

60

CHAPTER 2


RESPONSIBLE FOR DPO BIOSYNTHESIS IN

STREPTOMYCES POLYANTIBIOTICUS SPRT 2.1 Abstract ........................................................................................................................ 62

2.2 Introduction .................................................................................................................. 64

2.2.1 Biosynthesis of DPO ........................................................................................ 64

2.2.2 Isolation of genes involved in DPO biosynthesis ............................................ 67

2.3 Materials and Methods ................................................................................................. 70

2.3.1 Strains, media and growth conditions .............................................................. 70

2.3.2 Genomic DNA extraction ................................................................................ 70

2.3.3 Primer design ................................................................................................... 70

2.3.4 PCR protocols .................................................................................................. 74

2.3.4.1 A domain amplification ........................................................... 74

2.3.4.2 Cy domain amplification.......................................................... 74

2.3.4.3 Ammonia lyase gene amplification ......................................... 75

2.3.4.4 paaK gene amplification .......................................................... 75

2.3.4.5 Long range PCR ....................................................................... 76

2.3.4.6 Colony PCR ............................................................................. 76

2.3.5 Splinkerette method ......................................................................................... 77

2.3.6 Cloning and sequencing ................................................................................... 78

2.3.7 Sequence analysis ............................................................................................ 79

2.3.8 Southern hybridization ..................................................................................... 80

2.3.8.1 Restriction endonuclease digestion .......................................... 80

2.3.8.2 Probe preparation ..................................................................... 80

2.3.8.3 Southern blot hybridization...................................................... 81

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2.4 Results and Discussion ................................................................................................ 83

2.4.1 Isolation of the NRPS gene cluster .................................................................. 83

2.4.1.1 A domain amplification from S. polyantibioticus SPRT .......... 83

2.4.1.2 Southern hybridization using the phenylalanine-specific A

domain probe ........................................................................... 88

2.4.1.3 Cy domain amplification.......................................................... 89

2.4.1.4 NRPS domain amplification from Sts. Oxazolinicum.............. 92

2.4.2 Isolation of the genes involved in benzoic acid biosynthesis .......................... 92

2.4.2.1 Amplification of PAL/HAL ..................................................... 92

2.4.2.2 Southern hybridization using the encP gene probe .................. 94

2.4.2.3 Amplification of paaK ............................................................. 95

2.4.2.4 Southern hybridization using the paaK gene probe ................. 96

2.5 Conclusion ................................................................................................................... 98

2.6 Reference list ............................................................................................................... 99

Chapter 2 – Early attempts at isolating the gene cluster responsible for DPO biosynthesis in S. polyantibioticus SPRT

62

CHAPTER 2


RESPONSIBLE FOR DPO BIOSYNTHESIS IN

STREPTOMYCES POLYANTIBIOTICUS SPRT

2.1 ABSTRACT

To determine whether the hypothesis pertaining to the DPO biosynthetic pathway is correct,

the genes coding for benzoic acid synthesis and the DPO NRPS in the S. polyantibioticus SPRT

genome need to be identified. As benzoic acid synthesis is unusual in bacteria, the initial focus

was on detecting an NRPS gene in S. polyantibioticus SPRT with an A domain exhibiting a

binding pocket substrate specificity for phenylalanine or 3-hydroxyphenylalanine, as this

would most likely indicate an NRPS involved in the biosynthesis of DPO. This first step was

achieved by performing PCR amplification of NRPS A domain sequences, which led to the

identification of 12 unique NRPS A domains. One of the A domains was specific for

phenylalanine. This phenylalanine–specific domain (designated A-18) was used as a probe in

Southern hybridization experiments in an effort to identify larger DNA fragments surrounding

the A-18 NRPS gene cluster. However, no further sequence information could be obtained.

The identification of Cy domains in the genome of S. polyantibioticus SPRT was analysed in a

similar fashion to the A domains, as the presence of a Cy domain would be an indicator of

heterocyclization across the amide bond, a reaction required for the formation of an oxazole

ring. PCR primers specific for oxazole- and thiazole-producing Cy domains were designed in

an effort to identify Cy-domain-containing NRPS genes in S. polyantibioticus SPRT. The Cy-

domain primers were unsuccessful. Similar attempts were made at identifying genes involved

in the synthesis of benzoic acid in S. polyantibioticus SPRT, as the presence of a phenylalanine

ammonia-lyase (PAL) encoding gene would allow the synthesis of benzoyl-CoA for DPO


63

production. PCR primers were utilised to amplify the encP gene (encoding PAL) from

'Streptomyces maritimus' DSM 41777T and Southern hybridization confirmed the presence of

encP in this strain. In contrast, an encP homologue could not be detected in the genome of S.

polyantibioticus SPRT. As S. polyantibioticus SPRT appears not to possess a PAL gene, it was

suggested that this organism may produce benzoyl-CoA via the phenylacetate (PA) pathway

involved in the degradation of phenylalanine. The initial step of the PA pathway is catalyzed

by a PA-CoA ligase and degenerate primers were used to amplify a homologue of the gene,

paaK, encoding this enzyme in S. polyantibioticus SPRT. The presence of a paaK gene in S.

polyantibioticus SPRT was confirmed, suggesting that the PA pathway is present.


64

2.2 INTRODUCTION

2.2.1 BIOSYNTHESIS OF DPO

DPO is best known for its properties as a scintillator and as a high efficiency luminophore

(Ionescu et al., 2005; Semenova et al., 2004). It is produced for industry by chemical synthesis,

whereby it is used extensively in laser dyes and as a light activator for liquids (Semenova et

al., 2004; Adrova et al., 1957). However, the biological synthesis of DPO has never been

reported before and therefore its production by S. polyantibioticus SPRT is of great interest.

A biochemical pathway for the production of DPO by S. polyantibioticus SPRT has been

hypothesized whereby the compound is synthesized from starter units of benzoic acid (Figure

2.1A) and phenylalanine or 3-hydroxyphenylalanine (Figure 2.1B). Nucleophilic attack by the

α-amino group of 3-hydroxyphenylalanine on the electrophilic carboxyl group of benzoic acid

would result in the formation of an amide bond and the reaction intermediate benzoyl-β-

hydroxyphenylalanine (Figure 2.1C). This molecule is postulated to undergo a

heterocyclization or cyclodehydration reaction to create an oxazoline intermediate, which

would subsequently be oxidized to form an oxazole, 4-carboxy 2,5-diphenyloxazole (Figure

2.1D), by the nucleophilic attack of the phenylalanine β-hydroxy group on the carbonyl group

of the amide. The decarboxylation of the oxazole moiety would result in the formation of DPO

as the final product (Figure 2.1E).

The formation of the amide bond and subsequent heterocyclization reaction are assumed to be

catalyzed by an NRPS. The NRPS responsible for the biosynthesis of DPO is proposed to have

an A domain, plus ArCP, Cy, Ox, PCP and TE domains (Figure 2.2). The A domain would

recognise either 3-hydroxyphenylalanine or phenylalanine as the substrate and tether it to the

PCP domain. Although it is unclear whether the A domain would bind phenylalanine or β-

hydroxyphenylalanine, it seems more likely that phenylalanine would be the substrate, with

subsequent hydroxylation forming 3-hydroxyphenylalanine. If this is correct, then the DPO

NRPS would be expected to have an additional domain for a P450 monooxygenase to allow

for the β-hydroxylation of phenylalanine before the heterocyclization reaction (this P450

monooxygenase domain is not shown in Figure 2.2). The hydroxylation activity could also be

provided in trans. The ArCP domain would be responsible for loading benzoic acid.


65

The PCP domain would be responsible for keeping the 3-hydroxyphenylalanine intermediate

bound to the enzymatic machinery, while the ArCP domain would perform the identical

function in keeping the benzoyl intermediate bound. The Cy domain is proposed to perform

the dual function of facilitating the condensation between benzoic acid and 3-

hydroxyphenylalanine and carrying out the heterocyclization of benzoyl-β-

hydroxyphenylalanine to 4-carboxy 2,5-diphenyloxazole.

Furthermore, the Ox domain, which may exist as an external tailoring enzyme, would be

necessary for the oxidation of the hydrolytically labile oxazoline to form the oxazole moiety in

the heterocyclization reaction (the oxidation of the oxazolidine intermediate is not shown in

Figure 2.1). A decarboxylase reaction would be required to convert 4-carboxy 2,5-

diphenyloxazole to DPO. This decarboxylating activity could also be supplied in trans, as

occurs in curacin A biosynthesis in L. majuscula (Gu et al., 2006). Finally, the TE domain

would be involved in the release of DPO by breaking the covalent linkage between DPO and

the 4'-phosphopantetheine (4'-PP) thiol arm.


66

Figure 2.1 Proposed reaction scheme for the synthesis of DPO in S. polyantibioticus SPRT. (A) Benzoic

Acid, (B) 3-Hydroxyphenylalanine, (C) Benzoyl-β-Hydroxyphenylalanine, (D) 4-Carboxy 2,5-

Diphenyloxazole, (E) DPO. Reactions are shown by red arrows or lines, 1- Amide bond

formation, 2- Heterocyclization, 3- Decarboxylation. An NRPS is proposed to catalyse the

condensation of (A) and (B), as well as the proposed heterocyclization of (C) to form (D)

(Stegmann, 2011). Note that the oxazoline intermediate formed by the heterocyclization

reaction is not shown.


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Figure 2.2 The postulated NRPS module arrangement involved in the biosynthesis of DPO. The ArCP and

PCP domains are activated by the transfer of 4’-PP to the conserved serine residue on each

domain, which allows the covalent binding of benzoate (A) and 3-hydroxyphenylalanine (B),

as activated thioester derivatives. Domains: ArCP - aryl carrier protein, Cy – heterocyclization

domain, Ox – oxidation domain, PCP - peptidyl carrier protein domain, TE – thioesterase

domain. (Stegmann, 2011).

2.2.2 ISOLATION OF GENES INVOLVED IN DPO BIOSYNTHESIS

To assess whether the proposed biosynthetic pathway is correct, the genes required for the

synthesis of benzoic acid and the DPO NRPS, which are expected to be clustered on the S.

polyantibioticus SPRT genome, had to be identified.

The identification of an A domain in the genome of S. polyantibioticus SPRT, with a binding

pocket substrate specificity for phenylalanine, would indicate an NRPS that might be

responsible for the biosynthesis of DPO. PCR amplification, using suitable degenerate primers,

would allow for the detection of phenylalanine-specific A domains in S. polyantibioticus SPRT.

The substrate specificities of these PCR-amplified A domains could be determined by

comparison with the binding-pocket specificities of A domains for which the amino-acid

substrates are known. Larger fragments of the DPO biosynthetic gene cluster could then be


68

detected by Southern hybridization and further sequencing would reveal the remainder of the

genes constituting the cluster. Identification of the DPO biosynthetic gene cluster would add

to the handful of oxazole biosynthetic gene clusters characterised from actinomycetes

(Pulsawat et al., 2007; Zhao et al., 2006; Onaka et al., 2005).

The identification of a Cy domain in S. polyantibioticus SPRT may be analysed in a similar

fashion to the A domains and their presence would indicate NRPS enzymes involved in making

oxazoles or thiazoles. PCR primers specific for oxazole- and thiazole-producing Cy domains

may be used to amplify such domains.

In addition to searching for NRPS genes, the genes for benzoic acid biosynthesis need to be

identified. The presence of an orthologue of the encP gene, coding for phenylalanine ammonia-

lyase (PAL), in the genome of S. polyantibioticus SPRT would be of great interest, as PAL is a

key enzyme in the generation of benzoyl coenzyme A (benzoyl CoA) via trans-cinnamic acid

in a plant-like manner from phenylalanine in the biosynthesis of enterocin in ‘Streptomyces

maritimus‘strain DSM 41777T (Figure 2.3) (Moore et al., 2002; Hertweck & Moore, 2000). In

spite of its wide occurrence in fungi and plants, benzoic acid is an extremely rare bacterial

metabolite that has only been described in a few bacterial biosynthetic systems and as a central

intermediate of anaerobic aromatic molecule metabolism (Xiang & Moore, 2003). The

existence of an encP orthologue in the genome of S. polyantibioticus SPRT could be elucidated

using suitable PCR primers. Such an encP orthologue would be a strong candidate for

involvement in the biosynthesis of DPO.

If benzoic acid is not synthesized via a PAL-mediated pathway in S. polyantibioticus SPRT, it

could be synthesized via a novel variation on the phenylacetate pathway for the degradation of

phenylalanine. Besides the aerobic process catalysed by PAL in ‘S. maritimus’ strain DSM

41777T, other aerobic and anaerobic pathways for the production of benzoyl-CoA and

derivatives do exist, such as in the β-proteobacterium Azoarcus evansii, in which phenylacetic

acid is degraded via an anaerobic mechanism to benzoyl-CoA (Gescher et al., 2005). It has

been reported that phenylacetate-coenzyme A ligase (PA-CoA ligase) catalyses the initial

reaction in this pathway, which involves the activation of PA to PA-CoA. The gene coding for

PA-CoA ligase, paaK, has also been identified in Streptomyces species (Pometto and Crawford,

1985). Identification of a similar gene to paaK in S. polyantibioticus SPRT could indicate its


69

ability to synthesise benzoyl-CoA aerobically from PA (Figure 2.3B). Amino acid catabolism

has been linked to antibiotic synthesis in the production of macrolides in Streptomyces

ambofaciens and Steptomyces fradiae and therefore it is possible that an aromatic amino acid

degradation pathway could be involved in the production of a benzoic acid intermediate for

DPO biosynthesis (Tang et al., 1994). Alternatively, since the chorismate pathway is a common

pathway for generating molecules with benzene rings, such as shikimic acid, in bacteria (and

other organisms), S. polyantibioticus SPRT could perhaps also use a novel variant of one of the

aromatic biosynthetic pathways to generate benzoic acid (Figure 2.3D).

Figure 2.3 Biosynthetic pathways involved in the synthesis of benzoyl-CoA in ‘S. maritimus’ and plants

(route A), in anaerobic bacteria (route B), in fungi (route C) and from shikimic acid (route D)

(Hertweck & Moore, 2000).


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2.3 MATERIALS AND METHODS

2.3.1 STRAINS, MEDIA AND GROWTH CONDITIONS

‘S. maritimus’ DSM 41777T, Streptomyces virginiae NRRL B-1446T, Streptomyces avermitilis

MA-4680T, Streptomyces coelicolor A3(2) and Streptosporangium oxazolinicum JCM 17388T

were grown in yeast extract-malt extract broth (YEME; International Streptomyces Project

medium 2) (Shirling & Gottlieb, 1966) and S. polyantibioticus SPRT was grown in

Streptosporangium Medium (SM) (Pfefferle et al., 2000) for 7 days at 30oC with shaking. Gram

stains and single-colony streaking onto YEME or SM plates were performed to check for

contamination.

2.3.2 GENOMIC DNA EXTRACTION

Total genomic DNA (gDNA) was extracted from bacterial cell mass using the gDNA extraction

method of Wang et al. (1996), with the following modifications: 25 mg lysozyme/ml was used

instead of 5 mg/ml and the cells were incubated in the lysozyme buffer at 37 oC overnight

instead of for 30 min; isoamyl alcohol was omitted from the chloroform extraction step; and

the final precipitation of DNA was performed with the addition of one tenth of a volume of 3

M sodium acetate (pH 5.2) and one volume of room-temperature isopropanol. The

concentration of each gDNA sample was quantitated spectrophotometrically using the

Nanodrop® ND-1000 Spectrophotometer (Coleman Technologies Inc., USA) and analysed by

agarose gel electrophoresis. Visualization was performed with a Gel Doc XR (Bio-Rad

Laboratories Inc., USA) system and Quantity One Version 4.5.2 Software in order to assess

the quantity and integrity of the DNA samples. To confirm that the extracted gDNA was of

good quality, the 16S rRNA gene was PCR amplified as detailed in Cook & Meyers (2003).

gDNA samples were stored at 4 °C.

2.3.3 PRIMER DESIGN

All of the degenerate primers used in the early attempts to isolate the NRPS gene cluster are

listed in Table 2.1, accompanied by their sequences and binding positions. The A3F and A7R

primer set was designed to bind to the conserved motifs of actinomycete A domains, namely


71

A3 and A7, respectively (Ayuso-Sacido & Genilloud, 2005). This primer set was used to

amplify NRPS A domain fragments of approximately 700 bp in size.

A multiple amino acid sequence alignment of the Cy-domain regions of one oxazole and four

thiazole producing NRPSs from various bacterial strains (Table 2.2) obtained from the

GenBank database of the National Centre for Biotechnology Information (NCBI)

(http://www.ncbi.nlm.nih.gov/) was performed using DNAMAN version 4.13 (Lynnon

Biosoft, USA) in order to design the degenerate primer set CyF and CyR. The Cy domain

primer set amplifies a product of 1050 bp from S. polyantibioticus SPRT.

Another two Cy-domain forward primers, VVFTS CycF and QTPQV CycF, were designed

based on a multiple sequence alignment of the amino acid sequences used in the initial primer

design (Table 2.2) plus three new Cy domain sequences from S. coelicolor strain A3(2)

(GenBank accession number: NP_631722), Streptomyces roseosporus strain NRRL 111379

(GenBank accession number: ZP_04712035) and Streptomyces griseus subsp. griseus strain

NBRC 11350 (GenBank accession number: WP_012379765). These forward primers were

used in conjunction with the A domain reverse primer, A7R, and were expected to amplify a

PCR product of 1449 bp.

The primer set, PALHAL_F and PALHAL_R, was designed using DNAMAN from the

consensus sequence of a multiple sequence alignment of the PAL amino acid sequence from

‘S. maritimus’ DSM 41777T (GenBank accession number: AF254925) and the histidine

ammonia lyase (HAL) amino acid sequences from eleven Streptomyces species obtained from

the GenBank database (http://www.ncbi.nlm.nih.gov/) (Table 2.3). An amplification product

of approximately 350 bp was expected to be amplified from S. polyantibioticus SPRT. The

EncP-F and EncP-R primer set was designed to amplify a 721 bp encP fragment from the

biosynthetic gene cluster for benzoyl-CoA-derived enterocin in ‘S. maritimus’ DSM 41777T

(AF254925) (Stegmann, 2011).

The genes involved in the aerobic PA pathway are organized differently in different

Streptomyces strains and therefore two different sets of primers for the amplification of paaK

were designed. The primer set, Paak_AveF and Paak_AveR, was designed based on the

multiple sequence alignment of paaK nucleotide sequences from eight different Streptomyces

http://www.ncbi.nlm.nih.gov/


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strains obtained from the GenBank database (http://www.ncbi.nlm.nih.gov/), using DNAMAN

(Table 2.4). An amplification product of 490 bp was expected to be amplified from S.

polyantibioticus SPRT. In the same manner, the primer set, Paak_CoeF and Paak_CoeR was

designed based on the multiple sequence alignment of paaK nucleotide sequences from six

different Streptomyces strains using DNAMAN (Table 2.5). An amplification product of 709

bp was expected to be amplified from S. polyantibioticus SPRT.

Table 2.1. Oligonucleotide primers used in this study Primer Name Binding Position Primer Sequence (5'→3') A3F 1120-1142 a GCSTACSYSATSTACACSTCSGG

A7R 1820-1801 a SASGTCVCCSGTSCGGTAS

Cy-F 35-60b AGCCITTCYCSCTSACSSMBSTSCAG

Cy-R 1077-1054c AGGCAGGTCGGAGGTGAAGACGAC

VVFTS CycF 1274-1293d TSGTSTTCACSWSSIHSYTG

QTPQV CycF 1380-1398d TSWSSCAGACSCCSCAGGT

PALHAL_F 571-593e TACGGIGTSWVCACCRGBWTSGG

PALHAL_R 879-902e GIRCASCGBABSGARTASGCGTCC

Paak_AveF 559-583f CCBTCSTACMTGCTSACSCTSCTSGACG

Paak_AveR 1049-1022f GSAGSASGATCTCCTCGARCTGSSTGG

Paak_CoeF 315-340g CCRCGCAGGATSAYCATGTCGTCGC

Paak_CoeR 1024-1001g GCCTCCAGCGGNACSACSGGBCG

EncP-F 766-787e GACTCGCACCTGGCGGTCAAC

EncP-R 1486-1465e GTAGTCGGTGATGGTCTCGTC

M13F 2949-2972 CGCCAGGGTTTTCCCAGTCACGAC

M13R 197-176 TCACACAGGAAACAGCTATGAC aBased on the Brevibacillus brevis grsA1 sequence (GenBank accession number: D00519). bBased on the S. virginiae NRRL B-1446T virH sequence (Table 2.2). c Based on the S. verticillatus strain ATCC 15003 blmIV sequence (Table 2.2). d Based on the S. coelicolor A3(2) non-ribosomal peptide synthetase sequence (GenBank accession number: NP631722) e Based on the ‘S. maritimus’ DSM 41777T encP gene (Table 2.2) f Based on the S. avermitilis MA-4680T paaK gene (Table 2.2)

g Based on the S. coelicolor A3(2) paaK gene (Table 2.2)

Primers use standard ambiguity codes for nucleotides; I = inosine.

‘F’ denotes a forward primer and ‘R’ denotes a reverse primer.

http://www.ncbi.nlm.nih.gov/


73

Table 2.2. Bacterial species and genes used to design the CyF/CyR primers Species name Accession Number Gene Aromatic Compound

Streptoalloteichus hindustanus ATCC 31158 EF032505 tlmIV Tallysomycin Streptomyces atroolivaceus (no strain number given) AF484556 lnmI Leinamycin Streptomyces flavoviridis ATCC 21892 EU670723 zbmIV Zorbamycin Streptomyces verticillatus strain ATCC 15003 AF210249 blmIV Bleomycin Streptomyces virginiae AB283030 virH Virginiamycin M1

Table 2.3. Bacterial species and genes used to design the PALHAL primers Species name Accession Number Protein

‘Streptomyces maritimus’ AF254925 PAL Streptomyces sp. SirexAA-E AEN12031.1 HAL Streptomyces bingchenggensis BCW-1 ADI07714.1 HAL Streptomyces violaceusniger Tü 4113 AEM87830.1 HAL Streptomyces avermitilis MA-4680T WP_037644951.1 HAL

‘Streptomyces cattleya’ NRRL 8057 CCB76521.1 HAL

Streptomyces coelicolor A3(2) NP_629085.1 HAL

Streptomyces pratensis ATCC 33331 ADW03754.1 HAL

Streptomyces fradiae NRRL 18158 KDS89354.1 HAL

Streptomyces griseus NBRC 13350 BAG19440.1 HAL

Streptomyces scabiei 87.22 CBG72492.1 HAL

Streptomyces tsukubaensis NRRL 18488 EIF92105.1 HAL

Table 2.4. Bacterial species and genes used to design the Paak_Ave primers

Species name Accession Number Gene Streptomyces avermitilis MA-4680T BA000030 paaK ‘Streptomyces lividans’ TK24 ACEY01000018 paaK Streptomyces ambofaciens ATCC 23877 AM238663 paaK Streptomyces viridochromogenes DSM 40736 GG657757 paaK Streptomyces bingchenggensis BCW-1 CP002047 paaK Streptomyces albus J1074 DS999645, paaK Streptomyces clavuligerus ATCC 27064 CM000913 paaK Streptomyces sviceus ATCC 27064 CM000951 paaK


74

Table 2.5. Bacterial species and genes used to design the Paak_Coe primers

Species name Accession Number Gene Steptomyces coelicolor A3(2) AL645882.2 paaK Streptomyces hygroscopicus ATCC 53653 GG657754 paaK Streptomyces pratensis ATCC 33331 CP002475.1 paaK Streptomyces pristinaespiralis ATCC 25486 CM000950 paaK Streptomyces ghanaensis ATCC 14672 DS999641 paaK Streptomyces sp. SPB78 GG657742 paaK

2.3.4 PCR PROTOCOLS

All PCR amplifications were performed using a Techne TC512 Thermal Cycler fitted with a

heated lid and gradient sample block.

2.3.4.1 A DOMAIN AMPLIFICATION

The cycling conditions used for the amplification of the A domains from S. polyantibioticus

SPRT and Sts. oxazolinicum gDNA using the A3F/A7R primer set was as follows: initial

denaturation at 95 oC for 5 min, followed by 35 cycles of denaturation at 95 oC for 30 s,

annealing at 64 oC for 90 s and elongation at 72 oC for 4 min, with a final elongation at 72 oC

for 10 min. PCR reactions consisted of: 500 ng of DNA, 2 U SuperTherm Taq polymerase

(JMR Holdings, USA), 1.5 μM of each primer, 0.2 mM of each dNTP, 4 mM MgCl2 and 3 %

(v/v) glycerol in a total volume of 50 μl.

2.3.4.2 CY DOMAIN AMPLIFICATION

Cycling conditions for the amplification of the Cy domain from S. polyantibioticus SPRT

gDNA using the CyF/CyR primer set were similar to those used for amplification of the A

domain fragment (section 2.3.4.1), with the exception of the annealing temperature, which was

performed as a gradient ranging from 52 oC to 65 oC. PCR reactions were set up as described

in section 2.3.4.1, with the exception of the MgCl2 concentration, which ranged from 2 mM to

4 mM, the primer concentration, which ranged from 0.5 μM to 2.5 μM for each primer and the


75

glycerol concentration, which ranged from 2 % to 8 % (v/v). Template concentration was also

varied from 500 ng to 1500 ng. S. coelicolor A3(2) gDNA was used as a positive control.

Amplification using the VVFTS CycF/A7R and QTPQV CycF/A7R primer sets was performed

using the same cycling conditions and PCR reaction set up mentioned above.

2.3.4.3 AMMONIA-LYASE GENE AMPLIFICATION

Cycling conditions for the amplification of encP from S. polyantibioticus SPRT gDNA, using

the EncP-F/EncP-R primer set, consisted of the following: initial denaturation at 95 oC for 2

min, followed by 30 cycles of denaturation at 95 oC for 45 s, annealing at 60 oC for 30 s and

elongation at 72 oC for 70 s, with a final elongation at 72 oC for 5 min. PCR reactions contained:

500 ng of DNA, 1 U SuperTherm Taq polymerase (JMR Holdings, USA), 0.5 μM of each

primer, 0.2 mM of each dNTP and 4 mM MgCl2, in a total volume of 50 μl. ‘S. maritimus’

DSM 41777T gDNA was used as a positive control for the amplification of the encP fragment.

Cycling conditions using the primer set PALHALF/PALHALR were as follows: initial

denaturation at 95 oC for 5 minutes, followed by 35 cycles of denaturation at 95 oC for 30

seconds, annealing at 56 oC for 30 seconds and elongation at 72 oC for 60 seconds, with a final

elongation at 72 oC for 5 minutes. PCR reactions consisted of: 200 ng of DNA, 2 U SuperThem

Taq polymerase (JMR Holdings, USA), 0.5 μM of each primer, 0.2 mM of each dNTP and 3

mM MgCl2 in a total volume of 20 μl.

2.3.4.4 paaK GENE AMPLIFICATION

Cycling conditions for the amplification of paaK using the primer sets Paak_AveF/Paak_AveR

and Paak_CoeF/Paak_CoeR, from S. polyantibioticus SPRT were as follows: initial


annealing at 60 oC for 45 s and elongation at 72 oC for 60 s, with a final elongation at 72 oC for

5 min. PCR reactions consisted of: 400 ng of DNA, 2 U SuperThem Taq polymerase (JMR

Holdings, USA), 0.5 μM of each primer, 0.2 mM of each dNTP and 2 mM MgCl2 in a total

volume of 50 μl. S. coelicolor A3(2) and S. avermitilis MA-4680T gDNA were used as a


76

positive control for the amplification of the paaK fragment using the Paak_CoeF/Paak_CoeR

and Paak_AveF/Paal_AveR primer sets, respectively.

2.3.4.5 LONG RANGE PCR

In order to efficiently amplify large gDNA fragments of 5-25 kb in size, the Expand Long

Range dNTPack (Roche Diagnostics, Germany) was used. The cycling conditions for the

amplification of the DPO gene cluster using the A3F/Paak_AveR, Paak_AveF/A7R, VVFTS

CycF/A7R and QTPQV CycF/A7R primer sets were performed according to the

manufacturer’s instructions. Each PCR reaction consisted of 500 ng gDNA, 0.5 mM of each

dNTP, 0.5 µM of each primer, 8 % (v/v) DMSO, 2.5 mM MgCl2 and 3.5 U Expand Long Range

Enzyme mix in a total volume of 50 µl.

2.3.4.6 COLONY PCR

A colony PCR protocol was used to confirm the presence of cloned inserts in E. coli

transformants harbouring recombinant constructs. The PCR cycling conditions for the

amplification of these inserts was as follows: initial denaturation at 95 oC for 5 min, followed

by 35 cycles of denaturation at 95 oC for 30 s, annealing at 60 oC for 90 s and elongation at 72

oC for 60 s, with a final elongation at 72 oC for 10 min. PCR reactions consisted of: toothpick-

tip size amount of cell mass from an E. coli transformant colony, 2 U SuperThem Taq

polymerase (JMR Holdings, USA), 0.5 μM of each primer, M13F and M13R (Table 2.1), 0.8

mM of each dNTP and 3 mM MgCl2 in a total volume of 20 μl.

All PCR amplification products, including probes used for Southern hybridizations, were

resolved by electrophoresis alongside a λ-PstI molecular marker on 0.8 % agarose gels

containing 0.8 μg/ml ethidium bromide in order to analyse amplicon size and assess primer

specificity. The products were visualized using a long wavelength UV light box (Bio-Rad Gel

Doc EQ-system™, Bio-Rad Laboratories Inc., USA). For cloning, the fragments of interest

were excised from the gel and purified using the FavorPrep Gel/PCR Purification kit

(FavorGenTM, Germany) according to the manufacturer’s instructions. PCR products for

sequencing were purified using the MSB® Spin PCRapace kit (STRATEC Molecular,

Germany).


77

2.3.5 SPLINKERETTE METHOD

The splinkerette method, originally described by Devon et al. (1995), was used in an attempt

to obtain additional sequence information both upstream and downstream of the putative

phenylalanine-specific A domain sequence identified by amplification with the A3F/A7R

primer set. The protocol was modified by using an oligonucleotide adaptor sequence that

recognizes a XhoI overhang and XhoI-digested gDNA in the ligation reaction. A standard three

step PCR reaction using an annealing temperature of 55 oC was performed, as described in the

original method, using the splk0/PheAd GSP3 primer set. A second round of PCR was

performed using the same cycling conditions and PCR reagent concentrations, but the

splk1/PheAd GSP2 primer set was used instead and 10 µl of the initial PCR reaction was used

as the template. The primers are listed in Table 2.6.

The PCR amplification products were resolved by electrophoresis alongside a λ-PstI molecular

marker on a 1 % agarose gel, containing 0.8 μg/ml ethidium bromide, in order to analyse

amplicon size and primer specificity. The products were visualized with a long wavelength

UV light box (Bio-Rad Gel Doc EQ-system™, Bio-Rad Laboratories Inc., USA). The

fragments of interest were purified for sequencing as described in section 2.3.4.6.

Table 2.6 Oligonucleotide primers used in the splinkerette method

Oligonucleotide

name Primer Sequence (5'→3') Reference

Splnktop cgaatcgtaaccgttcgtacgagaattcgtacgagaatcgctgtcctctccaacgagccaaga Devon et al. (1995)

Splk0 Cgaatcgtaaccgttcgtacgagaa Devon et al. (1995)

Splk1 tcgtacgagaatcgctgtcctctcc Devon et al. (1995)

PheAd GSP2 tgaacgaggcgaactggagcacc This study

PheAd GSP3 ctgcggcgggatcgtcacatgg This study

Splnkxho tcgagcttggctcgtttttttttgcaaaaa This study


78

2.3.6 CLONING AND SEQUENCING

The amplification products obtained from the primer sets Paak_AveF/A7R (2.3.4.4) and

splk1/PheAD GSP2 (section 2.3.5) were purified using the MSB® Spin PCRapace kit

(STRATEC Molecular, Germany) and sent directly for sequencing, whereas the amplification

products obtained from the primer sets A3F/A7R, VVFTS/A7R, Paak_AveF/Paak_AveR,

PALHAL_F/PALHAL_R were ligated individually into the pGEM-T plasmid as described in

the pGEM®-T Easy Vector System kit (Promega, USA). The ligation reaction was incubated

at 22 °C for 14 h after which 10 ng of the reaction was transformed into E. coli α-Select Bronze

Efficiency Competent Cells (Bioline, UK) according to the manufacturer’s instructions. The

transformants were inoculated onto Luria-Bertani agar (LA) (Sambrook et al., 1989)

supplemented with 100 µg/ml ampicillin, 40 µg/ml X-gal and 0.2 mM IPTG and incubated at

37 °C for 18 h. Transformants harbouring recombinant pGEM-T constructs were identified by

blue/white selection and white colonies were subcultured onto fresh LA plates supplemented

with 100 µg/ ml ampicillin, 40 µg/ml X-gal and 0.2 mM IPTG and incubated at 37 °C for 18 h

to allow confirmation of the white phenotype. The presence of the desired inserts was

determined by performing colony PCR (section 2.3.4.6) using the M13F and M13R primer set

(Table 2.1).

Transformants identified as harbouring the correct recombinant constructs were inoculated into

5 ml Luria-Bertani broth (LB) containing 100 µg/ml ampicillin and grown overnight with

shaking at 37 °C. Thereafter, plasmid DNA was isolated using the NucleoSpin Plasmid

Isolation kit (Machery Nagel, Germany) according to the manufacturer’s instructions and

quantitated spectrophotometrically as described before (section 2.3.2). The cloned DNA

fragments were sequenced in both the forward and reverse direction using the M13F and M13R

primers (Table 2.1), by the dideoxy chain-termination method on an Applied Biosystems Big

Dye terminator v3.1 DNA sequencer using BIOLINE Half Dye Mix (Sanger et al., 1977)

(Macrogen Inc., South Korea).

S. polyantibioticus SPRT gDNA, digested with various restriction endonucleases (section

2.3.8.1), was excised from agarose gels and purified using the Favorgen Gel/PCR Purification

Kit (FavorgenTM, Germany), before ligating into the blue/white selection vector, pSK. One

microgram of pSK vector was digested individually with NotI, PstI or SacII overnight at 37 oC

using 1.5 U of each restriction endonuclease along with the appropriate restriction buffer. The


79

digested pSK vector was dephosphorylated using rAPid Alkaline Phosphatase (Roche,

Switzerland) according to the manufacturer’s instructions, but the incubation period at 37 oC

was extended to 24 h instead of the recommended 1 h. Subsequently, ligation of the digested

gDNA into the dephosphorylated pSK vector was performed according to the sticky-end

protocol for the Rapid DNA Ligation Kit (Thermo Fisher Scientific, USA) for 14 h at 4 oC,

after which 10 ng of the reaction was transformed into chemically competent E. coli cells.

Transformants were screened for inserts and sequenced as described above.

2.3.7 SEQUENCE ANALYSIS

All sequence chromatograms were viewed and edited using Chromas v2.01, (Technelysium,

Australia). DNA alignments, assembly of nucleotide sequences obtained by PCR

amplification, translations, in silico digestions and other analyses were performed using

DNAMAN v4.13 (Lynnon Biosoft, USA.).

The isolated DNA sequences were used to search for similar sequences in the GenBank

database (http://www.ncbi.blast.nlm.nih.gov/BLAST/) using the BLASTX algorithm (Altschul

et al., 1997). The NRPSpredictor2 program (Rausch et al., 2005) available online (http://www-

ab.informatik.uni-tuebingen.de/software/NRPSpredictor), was used to determine the signature

sequences of the binding pockets of the cloned A domains. The nucleotide sequence of each A

domain was translated and provided to the program, which identified the key binding-pocket

residues by an alignment with the PheA domain of GrsA and determined the probable

specificity of the A domain based on the biochemical and biophysical properties of the binding-

pocket residues.

http://www.ncbi.blast.nlm.nih.gov/BLAST/

http://www-ab.informatik.uni-tuebingen.de/software/NRPSpredictor

http://www-ab.informatik.uni-tuebingen.de/software/NRPSpredictor


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2.3.8 SOUTHERN HYBRIDIZATION

2.3.8.1 RESTRICTION ENDONUCLEASE DIGESTION

For Southern hybridizations using the paaK probe, S. polyantibioticus SPRT gDNA was

digested with the restriction endonucleases NotI & PstI and PstI & SacII, as well as with the

single restriction endonucleases NotI, PstI and SacII.

For Southern hybridization using the A domain probe, S. polyantibioticus SPRT gDNA was

digested with the single restriction endonucleases NotI, PstI and SacII.

For Southern hybridization using the encP probe, gDNA of S. polyantibioticus SPRT was

digested with the following restriction endonucleases: SphI & StuI, PvuII & SphI, AvrII & SphI

and AvrII & StuI. ‘S. maritimus’ DSM 41777T genomic DNA was digested with SphI & StuI.

Each reaction consisted of 50 μg of gDNA, 1.5 U of each restriction endonuclease and the

appropriate restriction buffer in a total volume of 50 µl. Digestions were performed overnight

at 37 oC.

2.3.8.2 PROBE PREPARATION

The recombinant constructs harbouring the phenylalanine-specific A domain insert (pGEMA-

18) and paaK gene insert (pGEM-PAAK) served as the templates for probe preparation using

the PCR DIG Probe Synthesis Kit (Roche). Additionally, PCR-amplified encP from ‘S.

maritimus’ DSM 41777T served as a template for probe preparation and was also used in a

Southern hybridization.

Probes for both the A-18 A domain and paaK gene were synthesized using the A domain

(section 2.3.4.1) and paaK (section 2.3.4.4) PCR protocols, respectively, and the plasmid

specific primers, M13F and M13R. The amplified encP gene probe was synthesized using the

DIG Probe Synthesis Kit (Roche, Switzerland), the encP PCR protocol (section 2.3.4.3) and

the EncP-F/EncP-R primer set.


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2.3.8.3 SOUTHERN BLOT HYBRIDIZATION

Restriction endonuclease digested S. polyantibioticus SPRT and ‘S. maritimus’ DSM 41777T

gDNAs were electrophoresed on 0.7 % agarose gels containing 0.8 μg/ml ethidium bromide

and individually blotted onto Hybond N+ membranes (Amersham Biosciences, UK) using a

Trans-blot® SD Semi-dry Transfer Cell (Bio-Rad Laboratories Inc., USA) for 1 h at 15 V and

a current of 355 mA.

Each membrane was air dried and placed into a sealable plastic bag with DIG Easy

Hybridization Buffer (Roche, Switzerland) (approximately 10 ml/100 cm2 of membrane). This

was followed by incubation with gentle shaking for 2 h at 56.3 oC for the A domain probe,

53.8 oC for the encP probe and 48 oC for the paaK probe (these being the calculated optimum

hybridization temperatures for each probe). The hybridization solution was prepared by adding

60 μl denatured probe to 20 ml hybridization buffer (Roche, Switzerland) and hybridization

was performed at the hybridization temperature overnight with gentle shaking. The

temperature of hybridization was calculated using the following formula:

Thyb = TM – (20oC to 25oC)

Where, TM = 49.82 + 0.41(% GC) – 600/ℓ TM – melting point of probe-target hybrid % GC – percentage G+C residues in the probe sequence Thyb – optimal temp for hybridization of the probe to target in DIG Easy Hybridization ℓ – length of the probe/hybrid in base pairs

After hybridization, the membrane was washed twice in low stringency buffer, containing 2 x

standard saline citrate (SSC; 0.3 M NaCl, 30 mM Na3C6H5O7) and 0.1 % sodium dodecyl

sulphate (SDS), at room temperature for 5 min with gentle shaking, followed by washing twice

in high stringency buffer (0.1 x SSC; 0.1 % SDS) at 68 oC for 15 min with gentle shaking. This

was followed by washing with washing buffer for 2 min at room temperature (0.5 M maleic

acid, pH 7.5; 0.3 % Tween 20) and subsequent blocking with 2 % skim milk for 2 h at room

temperature.

Following the blocking step, the membrane was incubated with the anti-DIG Alkaline

Phosphatase conjugate (Roche, Switzerland) at room temperature with shaking for 30 min. The

membrane was washed twice with washing buffer for 15 min at room temperature with shaking

to remove excess antibody.


82

Before detection, the membrane was equilibrated for 3 min in detection buffer (0.1 M Tris-

HCl, 0.1 M NaCl, pH 9.5) at room temperature. Detection was achieved by incubating the

membrane in 20 ml detection buffer containing 0.175 mg/ml 5-bromo-4-chloro-3-indolyl-

phosphate (BCIP) and 0.25 mg/ml 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium

bromide (MTT) in the dark at room temperature for 0.5-12 h. The reaction was stopped by

rinsing the membrane with Tris-EDTA buffer (10 mM Tris-HCl, 1 mM EDTA, pH 7.6) for 5

min, after which the result was digitally captured.


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2.4 RESULTS AND DISCUSSION

2.4.1 ISOLATION OF THE NRPS GENE CLUSTER

2.4.1.1 A DOMAIN AMPLIFICATION FROM S. POLYANTIBIOTICUS SPRT

The identification of an A domain in the genome of strain SPR with a binding pocket substrate

specificity for phenylalanine or 3-hydroxyphenylalanine could indicate that the A domain is

part of the NRPS responsible for the biosynthesis of DPO.

NRPS A domains were amplified from S. polyantibioticus SPRT by primers specific for A

domain conserved motifs (Ayuso-Sacido & Genilloud, 2005) (Figure 2.4). The amplified

products were individually cloned into the pGEM-T Easy vector, transformed into competent

E. coli cells and screened to confirm the presence of the correct size insert using colony PCR.

The inserts were sequenced before being subjected to protein BLAST (BLASTP) analysis in

order to confirm that they were A domains. Thirty-one recombinant constructs were identified

as carrying an insert (ranging in size from 688 to 729 nucleotide bases) with homology to

known A domains in the GenBank database (Table 2.7).

The first 9 amino acid residues of the binding-specificity code of the A domains were identified

for each unique sequence by aligning the protein sequence of each A domain against that of

the PheA domain of GrsA, in a similar manner to that shown in Figure 1.17. This resulted in

the identification of twelve unique amino acid binding pocket codes. Additionally, the A

domain protein sequences were inserted individually into the NRPSpredictor2 program, which

performs an alignment against the PheA domain of GrsA, but also analyses the physico-

chemical fingerprint of the residues lining the amino acid binding pocket to give an indication

of the most probable amino acid specificity of the binding pocket. Due to the occurrence of

relaxed substrate specificity in certain A domains, more than one amino acid substrate can be

predicted for any given A domain (e.g. substrates with similar physico-chemical properties)

(Rausch et al., 2005). The specificity binding code and likely amino acid substrate specificity

for the twelve unique A domains obtained from S. polyantibioticus SPRT are listed in Table

2.7.


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Figure 2.4 Gel electrophoresis of A domain amplicons from S. polyantibioticus SPRT amplified by PCR

using the degenerate primer set A3F/A7R. Lanes: 1- λ-PstI molecular marker, 2-6 – different

A domains amplified from S. polyantibioticus SPRT gDNA.

The sequences of the inserts in clones pGEMA-18 and pGEMA-66 were identical and were

determined by the NRPSpredictor2 to be specific for phenylalanine. Protein BLAST analysis

of the amino acid sequence of both inserts showed a high similarity to an A domain in

Granuliella mallensis MP5ACIX8 (GenBank accession number: YP_00507340.1) with an

amino acid similarity of 57 %, an A domain in Streptomyces griseus XYLEBKG1 (GenBank

accession number: YP_08236938.1) with an amino acid similarity of 60 % and an A domain

in Streptomyces netropsis (GenBank accession number: BAH_68437.1) with an amino acid

similarity of 54 %. Additionally, all of these BLASTP hits had an amino acid substrate

specificity for phenylalanine, as predicted by the NRPSpredictor2 program.

When comparing the amino acid specificity code of the pGEMA-18/pGEMA-66 clones to the

well-known phenylalanine-specific A domains of GrsA and BarG, there are differences

observed at the 236, 239, 299, 330 and 331 positions (Table 2.7). At position 236, pGEMA-

11.54

5.08 2.84 1.70

0.81 0.55

kb 1 2 3 4 5 6


85

18/A-66 differs from GrsA and BarG in having a cysteine residue instead of an alanine residue.

However, according to the gross clustering of NRPS substrates by chemical similarity, both

alanine and cysteine are classified as aliphatic, hydrophobic residues and thus could perform

the same function in the binding pocket interacting with non-polar, hydrophobic phenylalanine

(Rausch et al., 2005). At position 299, pGEMA-18/A-66 displays an alanine residue instead of

isoleucine in the GrsA sequence and valine in the BarG sequence. Isoleucine, alanine and

valine are, however, all non-polar amino acids, which may make them interchangeable, and

therefore they could perform the same function in the binding pocket in interacting with

phenylalanine. The same argument can also be used to explain the differences at position 330,

where GrsA displays an isoleucine residue in comparison to valine in both GrsA and pGEMA-

18/A-66.

The key differences are at position 239 where GrsA and BarG both display a tryptophan residue

in comparison to a glycine residue in pGEMA-18/A-66 and at position 331 where GrsA and

BarG both present a cysteine residue in contrast to aspartic acid in pGEMA-18/A-66.

However, both of these key differences occur at positions of medium to high variability and

thus should not have a large impact on the substrate affinity, as these residues may have

minimal interaction with the substrate amino acid.

From the specificity-conferring code and NRPS prediction software, it is possible to infer that

the pGEMA-18/pGEMA-66 A domain may be involved in the recognition and activation of

phenylalanine as a starter molecule in the biosynthesis of DPO. However, it is also possible

that the pGEMA-18/pGEMA-66 A domain may have a substrate specificity for amino acids

other than phenylalanine and this is due to the fact that the NRPSpredictor2 predicts aromatic

substrates less reliably due to the observed promiscuity of the A domains utilizing these

substrates (Rausch et al., 2005).

Furthermore, as serine residues are common amino acids for the biosynthesis of oxazoles, it is

feasible that any of the A domains specific for serine, such as the inserts in clones pGEMA-5,

A-7, A-12, A-15, A-22, A-36, A-51 and A-63 may activate serine as the starter unit instead of

phenylalanine, thereby utilising it in the biosynthesis of DPO (Roy et al., 1999). However, if

serine is recognised by the A domain involved in DPO biosynthesis, then it would require the


86

addition of a phenyl group to carbon-3 of the serine residue via an unusual β-phenylation

reaction.

The identification of the genes surrounding the phenylalanine A domain, as well as the A

domains specific for serine, would help to elucidate the DPO biosynthetic strategy. However,

attempts at isolating additional sequence information upstream and downstream of the A

domain specific for phenylalanine using the splinkerette method failed, as non-specific product

amplification was observed (data not shown).

Table 2.7 Specificity Binding Pocket Code and Amino Acid Specificity

Adenylation domain Source

Specificity Binding Pocket Code Residue and Positiona Amino Acid Specificityb

235 236 239 278 299 301 322 330 331 517

GrsA D A W T I A A I C K Phe, Trp, Phg

BarGc D A W T V A A V C K Phe, Trp, Phg

Clone pGEMAD-2 D V Q F N A H M V - Pro

Clone pGEMAD-16 D A F F L G V T F - Ile, Leu, Val

Clone pGEMA-1 D M V Q F G L V Y - Gly, Ala, Val

Clone pGEMA-5 D F W N V G M V H - Ser, Thr, Dht





Clone pGEMA-14 D M V Q F G L V H - Gly, Ala, Val

Clone pGEMA-15 D V W H F S L I D - Ser, Thr

Clone pGEMA-16 D A F F L G A T F - Ile, Leu, Val

Clone pGEMA-18 D C G T A A A V D - Phe, Trp, Phg, Tyr

Bht



Clone pGEMA-28 D M E N L G L I N - Orn, Lys, Arg

Clone pGEMA-31 D A F F L G A T F - Ile, Leu, Val

Clone pGEMA-32 G I Y H L G L L C - Dhpg, hpg

Clone pGEMA-33 G I Y H L G L L C - Dhpg, hpg



87


Clone pGEMA-48 - - - D V G F V - - NO HIT



Clone pGEMA-58 D A F F L G V T F - Val, Leu, Ile

Clone pGEMA-60 D A F F L G A A T - Val, Leu, Ile

Clone pGEMA-63 D V W H F S L I D Ser, Thr

Clone pGEMA-66 D C G T A A A V D - Phe, Trp, Phg, Tyr,

Bht




Clone pGEMA-74 D A A D V G F V D - Glu, Gln, Asp, Asn

Variabilityd % 3 16 16 39 52 13 26 23 26 0

a According to GrsA numbering b Predictions in order of decreasing preference, where A domain specificities have been clustered according to the physico-chemical fingerprint of the residues lining the amino acid binding pocket to give an indication of the most probable amino acid specificity of the binding pocket. c Part of the barbamide gene cluster in Lyngbya majuscule (GenBank accession number: AAN32981), a cyanobacterium. d The amount of variation observed at each amino acid position in the A domain substrate-determining signature sequence. The most variable positions (278 and 299) are considered to be ‘wobble’ positions (similar to the third position in DNA codons (Stachelhaus et al., 1999). Residue position 517 was not obtained for S. polyantibioticus SPRT A domain clones but, based on the high conservation of this residue, it is most likely lysine. Amino acid abbreviations use standard one and three letter codes. Dht - dehydrothreonine, Phg - L-phenylglycine, Hpg – hydroxyphenylglycine, Dhpg – dihydroxyphenylglycine. Highlighted rows indicate the clones carrying an A domain insert specific for phenylalanine.


88

2.4.1.2 SOUTHERN HYBRIDIZATION USING THE PHENYLALANINE-

SPECIFIC A DOMAIN PROBE

A Southern hybridization experiment was performed using a collection of single restriction

endonuclease digestions (PstI, NotI and SacII) of S. polyantibioticus SPRT gDNA in an attempt

to isolate DNA fragments large enough to provide additional sequence data on the NRPS gene

cluster involved in DPO biosynthesis. The phenylalanine-specific A domain probe detected

numerous bands of varying size, ranging from 0.7 kb to 4.5 kb, for each restriction

endonuclease in the Southern hybridization experiment (Figure 2.5). The presence of multiple

DNA fragments generated by the SacII and NotI digestions may be explained as a result of the

target A domain sequence being cleaved by these enzymes. An in silico digest of the S.

polyantibioticus SPRT phenylalanine (Phe)-specific A domain probe revealed that it is digested

by SacII at position 49 and 577 and by NotI at position 518. However, PstI does not cleave

within the Phe-specific A domain and thus it is proposed that the multiple hybridization bands

generated during this digestion may indicate the presence of other Phe-specific A domains in

the genome.

Due to the fact that the sizes of these bands were known, gel electrophoresis of gDNA digested

with PstI, SacII and NotI was performed and DNA of the appropriate size was purified and

cloned. Unfortunately, sequencing of the inserts did not yield any A-domain sequences, other

NRPS domains or their flanking regions.


89

Figure 2.5 Southern hybridization of restriction endonuclease digested S. polyantibioticus SPRT gDNA

using the Phe-specific A domain as a probe. Lanes 1-4 each contain 50 µg of S. polyantibioticus

SPRT gDNA digested singly with the following enzymes; Lanes: 1- PstI, 2- SacII 3- NotI, 4-

Unlabelled Probe (positive control).

2.4.1.3 CY DOMAIN AMPLIFICATION

Initially, the degenerate Cy domain PCR primer set, CyF/CyR, was designed based on

sequences from characterised Streptomyces and Streptoalloteichus thiazole and oxazole

producers and was expected to amplify a fragment of approximately 1050 bp from S.

polyantibioticus SPRT gDNA. However, there was no amplification of the correct-sized band

from either S. polyantibioticus SPRT gDNA or S. virginiae NRRL B-1446T (Figure 2.6A). It

should be noted that S. virginiae NRRL B-1446T may not be the same strain as that used for

1 2 3 4

4.5 2.9 0.7

kb


90

the design of the CyF/CyR primers (the papers describing virginiamycin M biosynthesis do not

specify which S. virginiae strain was used). As it is not known whether strain NRRL B-1446T

has the biosynthetic genes for virginiamycin M1, it may not have been a suitable positive

control.

Consequently, two new degenerate Cy domain PCR forward primers, VVFTS CycF and

QTPQV CycF, were designed based on a more comprehensive multiple sequence alignment

consisting of the original Cy domain sequences and the addition of three new Streptomyces Cy

domains. The new primers were used in conjunction with the A7R primer and were expected

to amplify a product of approximately 1449 bp. The reason for using a Cy-domain forward

primer with an A-domain reverse primer is that a typical linear NRPS elongation module

consists of the core domains arranged in the canonical order of C/Cy-A-PCP. An amplification

product of the correct size was observed using the VVFTS CycF/A7R primer set, but

sequencing revealed that a non-target product had been amplified. This was explained as being

due to the single VVFTS CycF primer on its own amplifying non-target sequences (Figure

2.6B, lane 9). The primer set QTPQV CycF/A7R failed to amplify the correct size product

(Figure 2.6C).

The lack of amplification of a Cy domain fragment may have been due to the fact that the target

sequence is not present in the genome of S. polyantibioticus SPRT, but a more likely scenario

is that the primers did not bind to the target sequences in S. polyantibioticus SPRT. A lack of

primer binding is plausible given the low degree of homology observed in the multiple

sequence alignments of Cy domains from the various thiazole and oxazole producers. The lack

of amplification in the case of the VVFTS CycF/A7R and QTPQV CycF/A7R primer sets may

be due to the fact that the NRPS biosynthetic strategy for DPO production may not follow the

conventional linear NRPS arrangement, but may in fact consist of a non-linear organization or

even contain unusual freestanding A or C/Cy domains. Investigation of this hypothesis is

described in the following chapter on the S. polyantibioticus SPRT genome sequence.


91

Figure 2.6 Gel electrophoresis of PCR amplified DNA from S. polyantibioticus SPRT using the degenerate

Cy domain primer sets (A) CyF/CyR, (B) VVFTS CycF/A7R and (C) QTPQV CycF/A7R. (A)

Lane 1: λ-PstI molecular marker, Lane 2-4: Amplification at annealing temperature of 52 oC

and increasing MgCl2 concentrations of 2, 3 and 4 mM respectively, Lane 5-7: Amplification at

annealing temperature of 58 oC and increasing MgCl2 concentrations of 2, 3 and 4 mM

respectively, Lane 8-10: Amplification at annealing temperature of 65 oC and increasing MgCl2

concentrations of 2, 3 and 4 mM respectively, Lane 11: No template control, Lane 12:

Amplification of Streptomyces virginiae NRRL B-1446T gDNA at annealing temperature of 52 oC and MgCl2 concentration of 3 mM . (B) Lane 1: λ-PstI molecular marker, Lane 2-4:

Amplification at annealing temperature of 55 oC and increasing MgCl2 concentrations of 2, 3

and 4 mM, respectively, Lane 5-7: Amplification of S. coelicolor (A3)2 gDNA at annealing

temperature of 55 oC and increasing MgCl2 concentrations of 2, 3 and 4 mM respectively, Lane

8: No template control, Lane 9: VVFTS CycF primer only, Lane 10: A7R primer only. (C) Lane

1: λ-PstI molecular marker, Lane 2: No template control, Lane 3-5: Amplification at annealing

temperature of 55 oC and increasing MgCl2 concentrations of 2, 3 and 4 mM respectively, Lanes

6-8: Amplification of S. coelicolor (A3)2 gDNA at annealing temperature of 55 oC and

increasing MgCl2 concentrations of 2, 3 and 4 mM respectively, Lane 9: QTPQV CycF primer

only.

11.54

5.08 2.84 2.56 1.99 1.70 1.16 0.81

0.51

A 1 2 3 4 5 6 7 8 9 10 11 12

kb 11.54 5.08 1.70 1.16

11.54 5.08

1.70 1.16

kb

kb

B

C

1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9


92

2.4.1.4 NRPS DOMAIN AMPLIFICATION FROM STS. OXAZOLINICUM

Sts. oxazolinicum was recently characterised as producing a novel group of antibiotics, the

spoxazomicins, which contain an oxazole moiety and are therefore likely to be produced non-

ribosomally (Inahashi et al., 2011). In light of this, it was decided that amplification of an A

domain and/or Cy domain from Sts. oxazolinicum would aid in the identification of the correct

A domain for DPO biosynthesis in S. polyantibioticus SPRT.

Subsequently, two unique A domains, bearing substrate specificity for serine and glycine

respectively, were identified in Sts. oxazolinicum following their amplification using the

A3F/A7R primer set. The Cy domain amplification using the VVFTS CycF/A7R and QTPQV

CycF/A7R primer sets was unsuccessful. Due to the fact that Cy domains are absolutely

necessary for the heterocyclization of serine or cysteine in the formation of an oxazole or

thiazole heterocyclic ring, respectively, it was decided that the A domains in S. polyantibioticus

SPRT that are specific for serine would remain of significant interest in the quest to uncover

the biosynthetic pathway involved in DPO production. Investigation into this hypothesis is

described in the following chapters.

2.4.2 ISOLATION OF GENES INVOLVED IN BENZOIC ACID BIOSYNTHESIS

2.4.2.1 AMPLIFICATION OF PAL/HAL

It has been shown that the presence of the PAL-encoding gene, encP, is absolutely required for

benzoyl-CoA formation in ‘S. maritimus’ DSM 41777T and therefore encP is a prime candidate

to screen for when searching for benzoyl-CoA biosynthetic potential (Xiang & Moore, 2003).

PCR amplification was performed using the designed encP primers on gDNA extracted from

S. polyantibioticus SPRT and ‘S. maritimus’ DSM 41777T. Amplification was observed for ‘S.

maritimus’ DSM 41777T gDNA resulting in a clear, single band of about 0.7 kb (Figure 2.7).

There was no similar amplification observed for encP amplification from S. polyantibioticus

SPRT. The lack of amplification from S. polyantibioticus SPRT DNA could be because the

organism does not contain an encP homologue. However, it could also be because the design

of the EncP-F/EncP-R primers was based on a single sequence (from ‘S. maritimus’ DSM

41777T), containing no variable nucleotide positions and therefore may not have bound

efficiently to the S. polyantibioticus SPRT encP homologue.


93

The PAL amino acid sequence from ‘S. maritimus’ DSM 41777T was used in a multiple

sequence alignment together with the HAL amino acid sequences from 11 Streptomyces strains

in order to design new degenerate primers for the amplification of a PAL/HAL from S.

polyantibioticus SPRT. The HAL sequences from various Streptomyces strains share a high

degree of homology with each other and to the PAL sequence of ‘S. maritimus’ DSM 41777T.

A 350 bp fragment was amplified from S. polyantibioticus SPRT gDNA, which was sequenced

and identified as a HAL after analysis using BLASTX. It was concluded that the existence of

a PAL in the genome of S. polyantibioticus SPRT is unlikely and therefore that the synthesis of

benzoic acid for incorporation into DPO does not proceed via a PAL-catalysed conversion of

phenylalanine to trans-cinnamic acid. Benzoic acid could be produced in a novel manner in S.

polyantibioticus SPRT, perhaps via the phenylalanine degradation pathway mentioned earlier

(section 2.2.2).


94

kb 11.54 5.08 2.84 2.56 1.99 1.70 1.16 0.81

Figure 2.7 Gel electrophoresis of PCR amplified encP and 16S rRNA genes from S. polyantibioticus SPRT

and ‘S. maritimus’ DSM 41777T. Lanes: 1- λ-PstI molecular marker, 2- ‘S. maritimus’ DSM

41777T amplified 16S rRNA gene, 3- S. polyantibioticus SPRT amplified 16S rRNA gene, 4-

‘S. maritimus’ DSM 41777T amplified encP, 5-6 S. polyantibioticus SPRT with no amplified

encP.

2.4.2.2 SOUTHERN HYBRIDIZATION USING THE ENCP GENE PROBE

Southern hybridization was performed using various pairwise restriction endonuclease

digestions of S. polyantibioticus SPRT gDNA along with a pairwise restriction endonuclease

digestion of ‘S. maritimus’ DSM 41777T gDNA. There was no hybridization observed for any

of the S. polyantibioticus SPRT genomic digests, while a weak hybridization band was observed

for the ‘S. maritimus’ DSM 41777T positive control (data not shown). The fact that no

hybridization signal was detected, corroborates the result of the PCR amplification experiment

(section 2.4.2.1) and suggests that there is no encP homologue in S. polyantibioticus SPRT.

However, neither the PCR nor the Southern hybridization result rules out the possibility that

there is an encP homologue in S. polyantibioticus SPRT involved in the synthesis of benzoic

1 2 3 4 5 6


95

acid, but which has a very dissimilar nucleotide sequence to the ‘S. maritimus’ DSM 41777T

encP gene.

2.4.2.3 AMPLIFICATION OF pAAK

Despite S. polyantibioticus SPRT appearing not to possess a PAL-like gene similar to encP, it

may produce benzoyl-CoA via the phenylacetate pathway used for the degradation of

phenylalanine. The initial step of the phenylacetate pathway is catalyzed by a PA-CoA ligase

and degenerate primers, paaK_AveF and paak_AveR, were used to amplify a 490 bp fragment

of the homologue of the gene, paaK, encoding this enzyme in S. polyantibioticus SPRT (Figure

2.8). The degenerate primer set, paaK_CoeF and paaK_CoeR did not amplify the expected

size product from S. polyantibioticus SPRT gDNA (data not shown). Additionally, based on

the fact that genes encoding functions for the biosynthesis of many antibiotics are clustered,

the primer sets A3F/paak_AveR and paak_AveF/A7R, were used in an effort to amplify larger

gDNA fragments containing both an NRPS A domain and the phenylacetate pathway gene

cluster (Ikeda et al., 1999). These attempts proved unsuccessful (data not shown).

The presence of paaK within the genome of S. polyantibioticus SPRT suggests that the

phenylacetate pathway is present, which was expected, as the prototrophic S. polyantibioticus

SPRT should have all the pathways for amino acid biosynthesis and degradation. However,

whether a derivative of this pathway is used by S. polyantibioticus SPRT to produce benzoyl-

CoA remains to be determined. It is possible that the genes involved in benzoic acid synthesis

are clustered together with the NRPS involved in DPO biosynthesis and therefore sequencing

further upstream and downstream of the amplified paaK fragment may help to uncover the

DPO NRPS.


96

Figure 2.8 Gel electrophoresis of PCR amplified paaK from S. polyantibioticus SPRT and S. avermitilis

MA-4680T. Lanes: 1- λ-PstI molecular marker, 2 - S. polyantibioticus SPRT amplified paaK

using 2 mM MgCl2 in PCR reaction, 3 - S. polyantibioticus SPRT amplified paaK using 3 mM

MgCl2 in PCR reaction, 4 - S. polyantibioticus SPRT amplified paaK using 4 mM MgCl2 in

PCR reaction 5- S. avermitilis MA-4680T amplified paaK.

2.4.2.4 SOUTHERN HYBRIDIZATION USING THE PAAK GENE PROBE

Southern hybridization using the paaK probe resulted in the detection of single bands of

approximately 1.8 kb for S. polyantibioticus SPRT gDNA digested with SacII, 2.5 kb for gDNA

digested with NotI and 4.5 kb for gDNA digested with PstI (Figure 2.9). S. polyantibioticus

SPRT digested gDNA fragments of about 1.8 kb and 2.5 kb were gel purified and cloned into

the plasmid vector pSK, before using colony PCR to identify clones carrying inserts.

Sequencing of the 1.8 kb insert revealed the presence of a monooxygenase gene and sequencing

of the 2.5 kb insert identified an A domain specific for proline. No clones containing the paaK

gene were identified. Thus, these results did not establish that the monooxygenase gene and

the proline A domain are near the paaK gene, nor that the paaK gene is near an NRPS

containing an A domain that activates phenylalanine.

1 2 3 4 5 kb 11.54

5.08 2.84 1.70

1.16 0.81 0.50


97

Figure 2.9 Southern hybridization of restriction endonuclease digested S. polyantibioticus SPRT genomic

DNA using the amplified paaK gene as a probe. Lanes 1-6 contain single and double

endonuclease digestions of 50 µg of S. polyantibioticus SPRT genomic DNA in each Southern

hybridization. Lanes: 1- NotI/PstI, 2- NotI, 3- PstI, 4- PstI/SacII, 5– SacII, 6- Unlabelled Probe

(positive control).

1 2 3 4 5 6 kb 4.5

2.5 1.8 0.5


98

2.5 CONCLUSION

In the efforts to isolate and identify the biosynthetic gene cluster for the production of DPO in

S. polyantibioticus SPRT, twelve unique A domains were identified. Importantly, one A

domain was predicted to be specific for the activation of phenylalanine, while two A domains

were predicted to be specific for serine. Serine could be involved in DPO biosynthesis due to

its known involvement in heterocyclic ring formation.

This chapter describes the extensive efforts to isolate additional sequence information upstream

and downstream of the NRPS A domains of interest, using the techniques of Southern

hybridization, the splinkerette method and long-range PCR. These efforts were all

unsuccessful. Furthermore, the inability to identify an NRPS Cy domain or any genes involved

in benzoic acid biosynthesis, led to the conclusion that a completely different approach was

required, namely, sequencing of the full S. polyantibioticus SPRT genome. The sequencing of

the genome and its annotation are described in the following chapter.


99

2.6 REFERENCE LIST

Adrova, N. A., Koton, M. M., & Florinsky, F. S. (1957). Preparation of 2, 5-diphenyloxazole and its scintillation efficiency in plastics. Russian Chemical Bulletin, 6(3): 394-395. Altschul, S.F., Madden, T.L., Schäffer, A.A., Zhang, J., Zhang, Z., Miller, W. & Lipman, D.J. (1997). Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic Acids Research, 25: 3389-3402. Ayuso-Sacido, G. & Genilloud, O. (2005). New PCR Primers for the sequencing of NRPS and PKS-I Systems in Actinomycetes: Detection and Distribution of These Biosynthetic Gene Sequences in Major Taxonomic Groups. Microbial Ecology, 49: 10-24. Cook A.E. & Meyers P.R. (2003). Rapid identification of filamentous actinomycetes to the genus level using genus-specific 16S rRNA gene restriction fragment patterns. International Journal of Systematic Evolutionary Microbiology, 6: 1907-1915. Devon, R.S., Porteous, D.J. & Brookes, A.J. (1995). Splinkerettes--improved vectorettes for greater efficiency in PCR walking. Nucleic Acids Research, 23(9): 1644–1645. Gescher, J., Eisenreich, W., Worth, J., Bacher, A. & Fuchs, G. (2005). Aerobic benzoyl-CoA catabolic pathway in Azoarcus evansii: studies on the non-oxygenolytic ring cleavage enzyme. Molecular Microbiology, 56(6): 1586-1600. Gu, L., Jia, J., Liu, H., Håkansson, K., Gerwick, W.H. & Sherman, D.H. (2006). Metabolic coupling of dehydration and decarboxylation in the curacin A pathway: functional identification of a mechanistically diverse enzyme pair. Journal of the American Chemical Society, 128: 9014-9015. Hertweck, C. & Moore, B.S. (2000). A plant-like biosynthesis of Benzoyl-CoA in the marine bacterium ‘Streptomyces maritimus’. Tetrahedron, 56: 9115-9120. Ikeda, H., Nonomiya, T., Usami, M., Ohta, T. & Mura, S.O. (1999). Organization of the biosynthetic gene cluster for the polyketide anthelmintic macrolide avermectin in Streptomyces avermitilis. Proceedings of the National Academy of Sciences of the USA, 96: 9509-9514. Inahashi, Y., Iwatsuki M., Ishiyama A., Namatame M., Nishihara-Tsukashima A., Matsumoto A., Hirose T., Sunazuka T., Yamada H., Otoguro K., Takahashi Y., Omura S. & Shiomi K. (2011). Spoxazomicins A-C, novel antitrypanosomal alkaloids produced by an endophytic actinomycete, Streptosporangium oxazolinicum K07-0460(T). The Journal of Antibiotics (Tokyo), 64(4): 303-307. Ionescu, S., Popovici, D., Balaban, A.T. & Hillebrand, M. (2005). Experimental and theoretical study of 2,5-diaryloxazoles whose aryl are para-substituted phenyl groups. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 62(1-3): 252-60.

Moore, B.S., Hertweck, C., Hopke, J.N., Izumikawa, M., Kalaitzis, J.A., Nilsen, G., O'Hare, T., Piel, J., Shipley, P.R., Xiang, L., Austin, M.B. & Noel, J.P. (2002). Plant-like biosynthetic pathways in bacteria: from benzoic acid to chalcone. Journal of Natural Products, 65: 1956-1962.

Onaka, H., Nakaho, M., Hayashi, K., Igarashi, Y. & Furumai, T. (2005). Cloning and characterization of the goadsporin biosynthetic gene cluster from Streptomyces sp. TP-A0584. Microbiology, 151: 3923-3933.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Iwatsuki%20M%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Ishiyama%20A%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Namatame%20M%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Nishihara-Tsukashima%20A%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Matsumoto%20A%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Hirose%20T%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Hirose%20T%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Sunazuka%20T%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Yamada%20H%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Otoguro%20K%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Takahashi%20Y%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Omura%20S%5BAuthor%5D&cauthor=true&cauthor_uid=21386848

http://www.ncbi.nlm.nih.gov/pubmed/?term=Shiomi%20K%5BAuthor%5D&cauthor=true&cauthor_uid=21386848


100

Pfefferle, C., Theobald, U., Gürtler, H. & Fiedler, H. (2000). Improved secondary metabolite production in the genus Streptosporangium by optimization of the fermentation conditions. Journal of Biotechnology, 80: 125-142. Pometto III, A.L., & Crawford, D.L. (1985). L-Phenylalanine and L-tyrosine catabolism by selected Streptomyces species. Applied Environmental Microbiology, 49(3): 727-729. Pulsawat, N., Kitani, S. & Nihira, T. (2007). Characterization of biosynthetic gene cluster for the production of virginiamycin M, a streptogramin type A antibiotic, in Streptomyces virginiae. Gene, 393: 31-42. Rausch, C. Weber, T., Kohlbacher, O., Wohlleben, W. & Huson, D.H. (2005). Specificity prediction of adenylation domains in nonribosomal peptide synthetases (NRPS) using transductive support vector machines (TSVMs). Nucleic Acids Research, 33: 5799-808.

Roy, R.S., Gehring, A.M., Milne, J.C., Belshaw, P.J. & Walsh, C.T. (1999). Thiazole and oxazole peptides: biosynthesis and molecular machinery. Natural Product Reports, 16: 249 – 263.

Sambrook, J., Fritsch, E.F. & Maniatis, T. (1989). Bacterial media, antibiotics and bacterial strains. Molecular Cloning, a laboratory manual, 2nd Ed. Cold Spring Harbour: Cold Spring Harbour Laboratory Press. Sanger, F., Nicklen, S. & Coulson, A., R. (1977). DNA Sequencing with chain-terminating inhibitors. Biotechnology, 24: 104-108. Semenova, O.N., Galkina, O.S., Patsenker, L.D., Yermolenko, I.G. & Fedyunyayeva, I.A. (2004). Experimental and theoretical investigation of the reaction of 2,5-diphenyl-1,3-oxazole and 2,5-diphenyl-1,3,4-oxadiazole dimethylamino derivatives with the Vilsmeier reagent. Functional Materials, 11: 67–75. Shirling, E. B. & Gottlieb, D. (1966). Methods for characterization of Streptomyces species. International Journal of Systematic Bacteriology, 16: 313-340. Stachelhaus, T., Mootz, H.D, & Marahiel, M.A. (1999). The specificity-conferring code of adenylation domains in nonribosomal peptide synthetases. Chemistry & Biology, 6: 493-505. Stegmann, D.E. (2011). The Investigation into the synthesis of 2, 5-diphenyloxazole in Streptomyces polyantibioticus SPRT. M.Sc. Thesis, Department of Molecular and Cell Biology, University of Cape Town. Tang, L., Zhang, Y. & Hutchinson, C.R. (1994). Amino Acid Catabolism and Antibiotic Synthesis: Valine Is a Source of Precursors for Macrolide Biosynthesis in Streptomyces ambofaciens and Streptomyces fradiae. Journal of Bacteriology, 176(19): 6107-6119. Wang, Y., Zhang, Z. & Ruan, J. (1996) A proposal to transfer Microbispora bispora (Lechevalier, 1965) to a new genus, Thermobispora gen. nov., as Thermobispora bispora combo. nov. International Journal of Systematic Bacteriology, 46: 933 – 938.

Xiang, L. & Moore, B.S. (2003). Characterization of Benzoyl Coenzyme A Biosynthesis Genes in the Enterocin-Producing Bacterium “Streptomyces maritimus”. Journal of Bacteriology, 185: 399-404.

Zhao, C., Ju, J., Christenson, S. D., Smith, W. C., Song, D., Zhou, X. Shen, B. & Deng, Z. (2006). Utilization of the methoxymalonyl-acyl carrier protein biosynthesis locus for cloning the oxazolomycin biosynthetic gene cluster from Streptomyces albus JA3453. Journal of Bacteriology, 188: 4142–4147.

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CHAPTER 3

STREPTOMYCES

POLYANTIBIOTICUS SPRT GENOME EXPLORATION

102

CHAPTER 3

STREPTOMYCES POLYANTIBIOTICUS SPRT GENOME

EXPLORATION 3.1 Abstract ...................................................................................................................... 103

3.2 Introduction ................................................................................................................ 105

3.3 Materials and Methods ............................................................................................... 111

3.3.1 Genomic DNA extraction .............................................................................. 111

3.3.2 Ethanol precipitation of genomic DNA ......................................................... 111

3.3.3 Genome sequencing and assembly using the 454 stand-alone platform ........ 111

3.3.3.1 Genome annotation ............................................................................ 111

3.3.4 Genome sequencing and assembly using a hybrid approach ......................... 112

3.3.4.1 Genome annotation ............................................................................ 112

3.3.4.2 Sequence analysis .............................................................................. 112

3.4. Results and Discussion .............................................................................................. 114

3.4.1 Initial genome sequencing using 454 technology .................. 114

3.4.2 S. polyantibioticus SPRT genome properties ......................... 114

3.4.3 Identification of the putative DPO biosynthetic gene cluster 117

3.4.4 Investigation into the putative DPO gene cluster .................. 119

3.4.4.1 A domain specificity .................................................. 124

3.4.4.2 Cy domains ................................................................ 126

3.4.4.3 PCP domains .............................................................. 135

3.4.4.4 Ox domains ................................................................ 139

3.4.4.5 TE domain .................................................................. 140

3.4.4.6 Genes involved in benzoic acid biosynthesis ............. 141

3.5 Conclusion ................................................................................................................. 144

3.6 Reference list ............................................................................................................. 145

Chapter 3 – Streptomyces polyantibioticus SPRT genome exploration

103

CHAPTER 3

STREPTOMYCES POLYANTIBIOTICUS SPRT GENOME

EXPLORATION

3.1 ABSTRACT

Initial efforts to sequence the S. polyantibioticus SPRT genome using the 454 pyrosequencing

approach proved unsuccessful. However, a hybrid approach using the “third generation” NGS

technology, PacBio, in combination with the Illumina MiSeq approach provided a draft

S. polyantibioticus SPRT genome sequence and with it the framework to identify the putative

DPO biosynthetic cluster. The draft S. polyantibioticus SPRT genome sequence was annotated

using antiSMASH 3.0, which identified 43 secondary metabolite gene clusters, thereby

revealing the potential of this strain to produce a range of biotechnologically pertinent

compounds.

A gene cluster within the draft S. polyantibioticus SPRT genome was identified as the putative

DPO biosynthetic gene cluster due to the fact that the NRPS genes in this cluster more closely

resembled the enzyme architecture hypothesized to be involved in DPO biosynthesis than any

other secondary metabolite cluster identified in the genome. The gene content and the

arrangement of the genes in the proposed DPO gene cluster was identical to the congocidine

biosynthetic gene cluster identified in Streptomyces ambofaciens ATCC 23877T.

Analysis of the NRPS domains within the putative DPO biosynthetic gene cluster revealed a

nonlinear NRPS initiation module, two lone C domains, a lone PCP domain and a lone A

domain encoded by an acyl-CoA synthetase. The in silico prediction of the substrate specificity

of the A domains within both the initiation module and the acyl-CoA synthetase proved

inconclusive due to the different predictions obtained from a range of NRPS prediction

programmes. However, it was hypothesized that both A domains could display a degree of


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relaxed amino acid substrate specificity, commonly observed in A domains displaying

specificity for aromatic amino acids, thereby allowing one A domain to activate phenylalanine

and the other to activate benzoic acid, in line with the hypothetical DPO biosynthetic scheme

presented in Chapter 2 (Figure 2.1). Furthermore, a phylogenetic analysis in combination with

an analysis of the conserved signature motifs frequently observed in NRPS domains revealed

the presence of S. polyantibioticus SPRT genes encoding putative Cy and TE domains within

the proposed DPO biosynthetic cluster. In addition, one PCP domain within the putative DPO

biosynthetic cluster was identified as likely to be active from the conserved signature motif

analysis, while a second PCP domain was classified as inactive due to the absence of a key

catalytic residue. Lastly, a biosynthetic pathway for benzoyl-CoA production in S.

polyantibioticus SPRT is proposed, based on the genome analysis.


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3.2 INTRODUCTION

The explosion in microbial genome sequencing over the past decade and a half, which has

appropriately been named the genomics era, has boosted the field of drug discovery from

microbial natural products. The chain-termination DNA sequencing method, also referred to

as dideoxy sequencing, developed by Sanger and colleagues in the 1970s has remained the

most commonly employed DNA sequencing technique to date. Recently, however, this method

has been partially superseded by several next-generation sequencing (NGS) technologies that

offer attractive increases in cost-effective sequence throughput (Morozova & Marra, 2008).

The automated chain-termination (Sanger) method is considered as a ‘first-generation’

technology, and newer methods are referred to as next-generation sequencing. These newer

technologies constitute various strategies that rely on a combination of template preparation,

sequencing and imaging, and genome alignment and assembly methods (Metzker, 2011;

Niedringhaus et al., 2011).

A major limitation of the chain-termination method is the requirement of in vivo PCR

amplification of DNA fragments that need to be sequenced, which is usually accomplished by

the laborious and labour intensive practice of cloning into bacterial hosts (Morozova & Marra,

2008). The 454 sequencing technology (Figure 3.1) developed by Roche Applied Science

(Penzberg, Germany) was the first NGS technology released onto the market and bypasses the

cloning requirement by using a highly efficient in vitro DNA amplification method known as

emulsion PCR (Tawflik & Griffiths, 1998). During emulsion PCR, individual DNA fragments

are linked to specific 454-adaptors bound to single streptavidin-coated beads which are

suspended in a water-in-oil emulsion, so that each bead with a single DNA fragment resides in

an individual aqueous droplet. These discrete emulsion droplets act as distinct amplification

reactors producing approximately 1 million clonal copies of a unique DNA template per bead

(Margulies et al., 2005). Each template-containing bead is then transferred into the well of a

picotiter plate and the templates are analysed using pyrosequencing. Instead of using

dideoxynucleotides to terminate the chain amplification, pyrosequencing technology relies on

the detection of pyrophosphate released during nucleotide incorporation and can be described

as a sequencing-by-synthesis technique that measures the release of inorganic pyrophosphate

(PPi) by chemiluminescence (Liu et al., 2012; Morozova & Marra, 2008). Briefly, the template

DNA is immobilized, and solutions of dNTPs are added sequentially; the release of PPi,


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whenever the complementary nucleotide is incorporated, is detectable by light produced by a

chemiluminescent enzyme, such as luciferase, present in the reaction mix. The sequence of the

DNA template is determined from a “pyrogram,” which corresponds to the order of correct

nucleotides incorporated. Since chemiluminescent signal intensity is proportional to the

amount of pyrophosphate released and hence the number of bases incorporated, the

pyrosequencing approach is prone to errors that result from incorrectly estimating the length

of homopolymeric sequence stretches (i.e. indels). The current state-of-the-art 454 platform

marketed by Roche Applied Science (Penzberg, Germany) is capable of generating 80–120 Mb

of sequence in 200- to 300-bp reads in a 4 h run (Morozova & Marra, 2008).

Figure 3.1 The 454 pyrosequencing approach. In this sequencing approach, DNA is isolated, sheared and

ligated to special adaptors. Emulsion PCR is then performed for clonal amplification after which the pyrosequencing reaction takes place using a mixture of the single-stranded DNA template, the sequencing primer, and the enzymes DNA polymerase, ATP sulfurylase, luciferase, and apyrase (Siqueira et al., 2012).


107

Other “second generation” NGS technologies include the Illumina MiSeq/Solexa approach,

which involves sequencing-by-synthesis of single-molecule arrays with reversible terminators.

A solid glass surface, known as a flowcell, which consists of an acrylamide coating, is used to

immobilize individual DNA molecules and bridge PCR amplification (PCR amplification that

occurs between primers bound to a surface) is used to amplify DNA into clusters of identical

molecules. This sequencing method is similar to the chain-termination method, in that it also

relies on dye terminator nucleotides incorporated in the sequence by a DNA polymerase.

However, Illumina/Solexa terminators are reversible, permitting polymerization to proceed

even after fluorophore detection. DNA sequencing commences with addition of the sequencing

primer, DNA polymerase, and four reversible dye terminators. Fluorescence is recorded after

incorporation by a four-channel fluorescent scanner (Quail et al., 2012; Siqueira et al., 2012;

Glenn, 2011). Furthermore, massively parallel sequencing by hybridization–ligation, which

was implemented in the supported oligonucleotide ligation and detection system (SOLiD), was

developed by Applied Biosystems (Waltham, USA) (Morozova & Maraa, 2008). This

approach involves fluorescent probes that undergo repetitive steps of hybridization and ligation

to complementary positions in the template strand, followed by fluorescence imaging to

identify the ligated probe (Loman et al., 2012). The ligation chemistry used in SOLiD is based

on the polony sequencing technique that was published in the same year as the 454 method

(Niedringhaus et al., 2011; Shendure et al., 2005). Meanwhile, “third generation” NGS

technologies include the PacBio Single Molecule, Real-Time (SMRT®) DNA Sequencing

System developed by Pacific Biosystems (Menlo Park, USA) that provides the longest read

lengths of any available sequencing technology (Roberts et al., 2013; Niedringhaus et al.,

2011). “Third-generation sequencing” is comprised of two main characteristics; 1) PCR is not

required before sequencing, which reduces DNA preparation time for sequencing and 2) the

signal is captured in real time, which means that the signal, no matter whether it is fluorescent

(Pacbio) or an electric current (Nanopore), is monitored during the enzymatic reaction of

adding a nucleotide to the growing complementary strand (Liu et al., 2012).

SMRT® sequencing is a sequencing-by-synthesis technology based on real-time imaging of

fluorescently tagged nucleotides as they are incorporated along individual DNA template

molecules. Due to the fact that the technology uses a DNA polymerase to drive the reaction,

and because it images single molecules, there is no degradation of signal over time (Roberts et

al., 2013). SMRT® is based on a chip pioneered by Levene et al. (2003) that contains an array

of zero-mode waveguides (ZMWs). Due to the fact that biological systems characteristically


108

pack their molecules at spacing much smaller than the wavelength of visible light, fluorescent

microscopy techniques that target single-molecule studies must overcome the diffraction-

limited resolution of conventional optical microscopy. Fluorescence microscopy techniques

such as ZMWs have been developed for this purpose and consist of simple nanostructures that

allow real-time observation of individual molecules at high concentrations (Zhu & Craighead,

2012).

During SMRT® sequencing, a single DNA polymerase is attached to the bottom of a well on a

SMRT® Cell, and the millions of ZMWs create an illuminated volume that is small enough to

observe the incorporation of a single nucleotide. Each time a nucleotide is added to the DNA

at the bottom of the well, the dye is detected before being cleaved off and diffusing away (Liu

et al., 2012; Levene et al., 2003). The camera inside the instrument computer captures the

signal in real-time observation (Mardis, 2013; Liu et al., 2012).

The Ion Torrent platform, marketed by Life Technologies (Carlsbad, USA), uses a sequencing

strategy similar to the 454 platform, except that hydrogen ions (H+) are detected instead of a

pyrophosphatase cascade. The use of H+ means that no lasers, cameras or fluorescent dyes are

needed (Glenn, 2011). Furthermore, this platform utilizes semiconductor technology that

detects the release of protons as nucleotides are incorporated during DNA synthesis. DNA

fragments with specific adapter sequences are linked to and then clonally amplified by

emulsion PCR on the surface of 3-micron diameter beads, known as Ion Sphere Particles. The

templated beads are loaded into proton-sensing wells that are fabricated on a silicon wafer and

sequencing is primed from a specific location in the adapter sequence. As sequencing proceeds,

each of the four bases is introduced sequentially and if bases of that type are incorporated,

protons are released and a signal is detected proportional to the number of bases incorporated

(Quail et al., 2012).

Nanopore sequencing is another “third generation sequencing” method that relies on the transit

of a DNA molecule or its component bases through a biological nanopore. The bases are

detected by their effect on an electrical current or optical signal (Steinbock & Radenovic, 2015;

Schadt et al., 2010).


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The increase in speed and decrease in the cost of genome sequencing, as well as the rise of

metagenomic sequencing projects, have been the key driving factors for the revolution in the

field of microbial drug discovery. Particularly, it has been revealed that streptomycetes still

represent a major source for the discovery of novel natural products due to the wealth of NRPS

and PKS structural diversity that they encode (Boddy, 2014). This was emphasized by the

complete genome sequence of S. coelicolor strain A3(2), which revealed the unexpected

potential of this microorganism to produce natural products that were undetectable by classical

screening methods, such as bioactivity-guided fractionation of crude fermentation broth

extracts and chemical screening methods (Aigle et al., 2014; Bachmann et al., 2014).

Indeed, whereas just five secondary metabolites were identified over 50 years using classical

screening approaches, the advancement in genome sequencing technologies and bioinformatics

has revealed that S. coelicolor A3(2) has the capability to produce almost 20 additional natural

products (Bentley et al., 2002).

Furthermore, the mining of the genome of S. ambofaciens ATCC 23877T which, for many

decades, was only known to produce the macrolide spiramycin and the pyrrolamide

congocidine, has allowed for the identification of an additional 23 gene clusters putatively

involved in the production of a variety of other secondary metabolites.

Importantly, it is critical to note that this situation is not specific to S. coelicolor A3(2) and

S. ambofaciens ATCC 23877T, as both complete and partial genome sequencing of numerous

streptomycetes has shown that they all contain a large number of cryptic secondary metabolite

gene clusters. Thus, these strains contain genes that are not expressed under standard laboratory

conditions or the products are formed at a level too low to be detected in laboratory growth

conditions (Aigle et al., 2014; Ikeda et al., 2014, Jensen et al., 2014, Nett et al., 2009; Baltz,

2008).

The annotation of sequenced genomes from several Streptomyces species has shown that a

single strain can carry more than 30 secondary metabolite gene clusters, thereby supporting the

idea that the biosynthetic potential of this bacterial genus is far from being fully exploited

(Aigle et al., 2014).


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The recent advances in genome sequencing are rapidly changing the field of bacterial natural

products research by providing opportunities to assess the biosynthetic potential of strains prior

to chemical analysis or biological testing. Furthermore, the easy access to sequence data is

driving the development of new bioinformatic tools and methods to identify the products of

silent or cryptic pathways (Jensen et al., 2014; Bérdy, 2012).

Indeed, automatic bioinformatics platforms, such as antiSMASH 3.0 (Weber et al., 2015),

allow the efficient detection of secondary metabolite gene clusters belonging to a range of

different classes of natural products and also facilitate the semi-automated prediction of the

structure of the natural products encoded by these secondary metabolite blueprints (Bachmann

et al., 2014). It has been reported that antiSMASH analysis, which has become the gold

standard for mining secondary metabolite gene clusters in genome sequences, compares

favourably with high-quality, detailed manual annotation of bacterial whole genomes and

provides a more detailed description of individual gene clusters identified than NaPDOS

(Ziemert et al., 2012) and NP.searcher (Li et al., 2009) (Boddy, 2014; Harrison & Studholme,

2014). Furthermore, the ClusterBlast and SubClusterBlast tools available within antiSMASH

enable rapid identification of unique gene clusters from sequence data sets (Boddy, 2014).

However, a concern with automated genome analysis is that gene clusters located near to each

other, may be merged into superclusters, as occurs with the salinilactam gene cluster (Udwary

et al., 2007), as antiSMASH defines clusters as groups of signature genes within 10 kb of each

other and extends the cluster 20 kb on each side of the last signature gene to delineate the

boundaries of PKS and NRPS biosynthetic gene clusters (Boddy, 2014; Medema et al., 2011).

Nevertheless, the recent innovation in genome sequencing has disclosed the astonishing wealth

of new polyketide and non-ribosomal peptide natural product diversity to be mined from

genetic data and these web-based bioinformatics tools can play a key role in guiding the

discovery of novel natural products in genome mining projects, enabling the focus on

biosynthetic gene clusters likely to encode new natural product diversity (Boddy, 2014).


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3.3.1 GENOMIC DNA EXTRACTION

The gDNA for both 454 sequencing and sequencing using the hybrid approach was extracted

from S. polyantibioticus SPRT bacterial cell mass using the gDNA extraction method described

in section 2.3.2.

3.3.2 ETHANOL PRECIPITATION OF GENOMIC DNA

Total gDNA isolated from S. polyantibioticus SPRT was subjected to ethanol precipitation so

that it would be stable against any fluctuations in temperature during transportation to ChunLab

(Seoul, South Korea) for hybrid genome sequencing. Briefly, 1 µl of 10 mg/ml glycogen was

added to 100 µl of 1 µg/µl gDNA sample, followed by the addition of 10 µl of 3 M sodium

acetate (pH 5.2), after which the sample was briefly vortexed. Three hundred microliters of

100 % ethanol was then added to the sample, which was vortexed briefly again. The sample

was placed on ice for 30 min and thereafter transported to the sequencing facility.

3.3.3 GENOME SEQUENCING AND ASSEMBLY USING THE 454 STAND-ALONE

PLATFORM

The first attempt at sequencing the S. polyantibioticus SPRT genome was performed at the Next

Generation Sequencing Facility at the University of the Western Cape (Cape Town, South

Africa) using a 454 GS FLX Titanium system (Roche, Switzerland). The Newbler Assembler

2.6 (Roche, Switzerland) was used in an attempt to assemble the reads.

3.3.3.1 GENOME ANNOTATION

Initially, the genes in each of the individual contigs obtained from the 454 genome sequencing

were predicted using the Rapid Annotation using Subsystem Technology (RAST) 2.0 server

database (Overbeek et al., 2014). Additionally, the sequences of the contigs were aligned and

edited using Sequencher version 5.1 (Genecodes Corporation, USA) in order to achieve

assembly.


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3.3.4 GENOME SEQUENCING AND ASSEMBLY USING A HYBRID APPROACH

The genome of S. polyantibioticus SPRT was sequenced at ChunLab (Seoul, South Korea)

using a combination of an Illumina Miseq PE-300 system (Illumina, USA) with 2 × 300 paired-

end reads and a PacBio RSII system (Pacific Biosciences, USA). The Illumina and PacBio

reads were assembled using CLC Genomics Workbench 7.0.4 (CLCbio, Denmark) and PacBio

SMRT Analysis 2.2.0, respectively, and used to construct the draft S. polyantibioticus SPRT

genome sequence.

3.3.4.1 GENOME ANNOTATION

The genes in the assembled genome were predicted using the Rapid Annotation using

Subsystem Technology (RAST) 2.0 server database (Overbeek et al., 2014) and the gene-caller

GLIMMER 3.02 (Delcher et al., 2007). The predicted ORFs were annotated by searching

clusters of orthologous groups (COGs) using the SEED database (Disz et al., 2010; Tatusov et

al., 1997). CLgenomics™ 1.06 (ChunLab) was used to visualize the genomic features, while

protein homologies and conserved domains were analysed by application of BLASTp and the

Conserved Domain Database (CDD; Marchler-Bauer et al., 2011). AntiSMASH 3.0 (Weber

et al., 2015) was used to identify secondary metabolite clusters within the draft genome, while

the NRPSpredictor2 program (Röttig et al., 2011) in combination with the latent semantic

indexing (LSI) model (developed by Baranasic et al., 2013), the NRPS/PKS prediction server

(Bachmann & Ravel, 2009), the Non-Ribosomal Peptide Synthase Substrate Predictor

(NRPSsp) (Preito et al., 2012) and the Stachelhaus code (Stachelhaus et al., 1999) were used

to predict the substrate specificity of all contigs containing NRPS A domains. The NaPDos

tool (available via http://napdos.ucsd.edu/) was utilized in the analysis of all NRPS C domains

(Ziemert et al., 2012). Other sequence features were identified using RNAmmer (Lagesen et

al., 2007) and tRNAscan-SE (Lowe & Eddy, 1997).

3.3.4.2 SEQUENCE ANALYSIS

For the phylogenetic analysis of the putative domains identified as members of the DPO

biosynthetic cluster, amino acid sequences of each separate domain, A, C, PCP, Ox and TE,

were obtained from the detailed antiSMASH 3.0 annotation and aligned against homologous

amino acid sequences that were selected from the GenBank database

(http://www.ncbi.nlm.nih.gov/). The sequences were aligned using the Multiple Sequence


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Comparison by Log-Expectation (MUSCLE) algorithm (Edgar, 2004) in Molecular

Evolutionary Genetics Analysis (MEGA) version 6.0 (Tamura et al., 2013).

Phylogenetic analyses were performed by construction of unrooted phylogenetic trees using

the neighbour joining (Saitou & Nei, 1987), maximum likelihood (Jones et al., 1992) and

maximum parsimony (Takahashi & Nei, 2000) methods. A bootstrap test was employed, based

on 1000 replicates, to assess the reliability of the topology of each phylogenetic tree. All

columns in the alignment containing gaps and missing data were eliminated from the dataset.

Additionally, the conserved NRPS signature motifs, as described by Schwarzer et al. (2003),

were examined in the multiple sequence alignment of the putative S. polyantibioticus SPRT A,

C, PCP, Ox and TE domains in comparison to homologous reference sequences obtained from

the GenBank database (http://www.ncbi.nlm.nih.gov/).


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3.4.1 INITIAL GENOME SEQUENCING USING 454 TECHNOLOGY

The 454 pyrosequencing platform generated 7 178 853 bp of S. polyantibioticus SPRT genome

sequence consisting of 3553 contigs, however, the de novo assembly of the contigs, ranging in

size from 100 bp to 78 914 bp, proved unsuccessful. This was attributed to the inability of the

sequence assembly program to deal with the highly repetitive strings of G + C residues.

In an attempt to manually assemble the contigs, the sequence analysis program Sequencher

version 5.1 (Genecodes Corporation, USA) was employed, but this strategy was unsuccessful.

After trying to work with the 454 sequence data for over a year, it was concluded that the reason

the genome-sequence contigs could not be assembled was due to there being pieces of the

genome missing. Indeed, S. polyantibioticus SPRT has been characterized to use salicin and

myo-inositol as sole carbon sources (Le Roes-Hill & Meyers, 2009) yet the RAST analysis

showed that critical enzymes, such as the protein-Nπ-phosphohistidine sugar

phosphotransferase (EC 2.7.1.69) involved in the catabolism of salicin to salicin-6-phosphate

and all of the enzymes involved in myo-inositol metabolism were absent. Additionally,

S. polyantibioticus SPRT has been characterized to use L-phenylalanine as a sole nitrogen

source (Le Roes-Hill & Meyers, 2009), yet the deaminating phenylalanine dehydrogenase

(EC 1.4.1.20), critical for its catabolism, was also absent from the sequencing data. The absence

of these key enzymes, in addition to critical enzymes involved in fatty acid metabolism,

menaquinone biosynthesis and glycolysis/gluconeogenesis, prompted the decision to

re-sequence the S. polyantibioticus SPRT genome using a different platform.

3.4.2 S. POLYANTIBIOTICUS SPRT GENOME PROPERTIES

The Illumina platform provided 482.63-fold coverage (for a total of 15 763 940 sequencing

reads) of the genome, while the PacBio platform generated a 38.13-fold coverage of the

genome (for a total of 65 082 sequencing reads). The assembled sequences from the two

approaches resulted in 1 scaffold that consisted of 12 large contigs, while the assembled draft

genome comprised a chromosome (Appendix A) with a length of 8 821 522 bp and 71.53 % G

+ C content (520.76-fold coverage), which is lower than the 74.4 ± 0.2 mol% determined by

the thermal denaturation method (Le Roes-Hill & Meyers, 2009). The draft genome sequence


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contained 8148 ORFs, of which the majority (5360, 66%) were assigned putative functions

according to the COG functional categories (Table 3.1). In addition, the draft genome sequence

consisted of 69 tRNA genes and 24 rRNA genes. Le Roes-Hill and Meyers (2009) reported 7

rRNA operons in the description of Streptomyces polyantibioticus sp. nov. The existence of

69 tRNA genes is somewhat surprising considering the fact that there are 64 possible codons

(of which three are stop codons and would not be involved in the activation of amino acids). It

may be noted that the Streptomyces davawensis JCM 4913 genome sequence also revealed the

presence of 69 tRNA genes, which suggests that the occurrence of more than the usual 30-40

tRNA encoding genes in bacterial cells is not uncommon (Jankowitsch et al., 2012; Lodish et

al., 2000).


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Table 3.1. Number of genes associated with the general COG functional categories Description Value % of totala

Translation, ribosomal structure and biogenesis

215

4.01

Transcription 633 11.81

Replication, recombination and repair 169 3.15

Cell cycle control, cell division, chromosome partitioning 41 0.76

Posttranslational modification, protein turnover, chaperones 147 2.74

Cell wall/membrane/envelope biogenesis 302 5.63

Cell motility 8 0.15

Inorganic ion transport and metabolism 177 3.30

Signal transduction mechanisms 356 6.64

Energy production and conversion 304 5.67

Carbohydrate transport and metabolism 461 8.60

Amino acid transport and metabolism 490 9.14

Nucleotide transport and metabolism 125 2.33

Coenzyme transport and metabolism 226 4.22

Lipid transport and metabolism 321 5.99

Secondary metabolite biosynthesis, transport and catabolism 159 2.97

General function prediction only 766 14.29

Function unknown 460 8.58

a The total is based on the 8148 ORFs identified in the annotated genome.


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3.4.3 IDENTIFICATION OF THE PUTATIVE DPO BIOSYNTHETIC GENE

CLUSTER

AntiSMASH 3.0 identified 43 gene clusters encoding secondary metabolites in the draft

genome of S. polyantibioticus SPRT, revealing the potential of this strain to produce a wide

range of biotechnologically relevant compounds: 4 clusters for lantipeptides, 6 clusters for

NRPSs, 1 cluster for a siderophore, 10 clusters for PKSs, 2 hybrid NRPS-PKS clusters, 6

clusters encoding terpenes, 2 clusters encoding bacteriocins, 2 clusters encoding melanin, 1

cluster encoding a phenazine/melanin hybrid, 1 cluster encoding a β-lactam, 1 cluster encoding

a terpene/lantipeptide hybrid, 1 cluster encoding a lantipeptide/lassopeptide/terpene hybrid, 1

cluster encoding an aminoglycoside/aminocyclitol, 1 cluster encoding a butyrolactone, 1

cluster encoding an ectoine and 3 unidentified clusters.

The putative biosynthetic scheme for the production of DPO proposes that a single NRPS

condenses a molecule of benzoic acid with 3-hydroxyphenylalanine. This NRPS is proposed

to possess a single A domain, plus ArCP, Cy, Ox, PCP and TE domains (Figure 2.2). In light

of this hypothesis, the antiSMASH results were analysed to identify the genes involved in the

biosynthesis of DPO amongst the NRPS gene clusters.

The secondary metabolite gene cluster spanning the region located from nucleotide 637827-

688770 (Appendix A) of the draft S. polyantibioticus SPRT genome consisted of a linear NRPS

encoding 3 A domains with two of them predicted to be specific for the activation of ornithine

and one specific for the activation of threonine. Additionally, all of the genes comprising this

cluster shared homology to the genes comprising the coelichelin biosynthetic cluster identified

in S. coelicolor A3(2).

An NRPS gene cluster spanning the region located from nucleotide 669778-735243 (Appendix

A) overlapped the NRPS cluster mentioned above, but consisted of 2 A-PCP di-domains and

freestanding, adjacently encoded A, C and PCP domains. The three A domains were predicted

to be specific for the activation of threonine, proline or valine and leucine, isoleucine, isovaline

or 2-amino-butyric acid, respectively. The composition of this gene cluster was most similar

in gene content to the tobramycin biosynthetic gene cluster identified in Streptoalloteichus

tenebrarius, as 24 % of the S. polyantibioticus SPRT genes shared homology to genes within

this cluster according to the antiSMASH analysis.


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Due to the fact that both of the NRPS gene clusters mentioned above consisted of 3 A domains

each, of which none were predicted to be specific for the activation of aromatic amino acids

such as phenylalanine or 3-hydroxyphenylalanine, and because the homologous gene clusters

encode coelichelin and tobramycin, neither of which contains an aromatic heterocycle, they

were dismissed as putative DPO biosynthetic clusters.

The secondary metabolite gene cluster spanning the region located from nucleotide 3093585 –

3154158 (Appendix A) consisted of 4 linear NRPS modules in close proximity and also

overlapped an upstream secondary metabolite cluster encoding a terpene, which was predicted

to encode a compound of complex molecular structure. Indeed, the gene content of this gene

cluster shared the highest homology (12 %) with the biosynthetic gene cluster encoding the

cyclic depsipeptide, skyllamycin A, isolated from Streptomyces sp. Acta 2897. The

skyllamycin A structure consists of a cinnamoyl side chain and incorporates a large number of

β-hydroxylated amino acids as well as an unusual α-hydroxyglycine moiety as a rare structural

modification (Pohle et al., 2011). This structure does not bear any resemblance to that of DPO

and this gene cluster was therefore dismissed as a putative DPO biosynthetic cluster.

Similarly, the secondary metabolite cluster spanning the region from nucleotide 3320540 –

3386004 (Appendix A) consisted of 4 linear NRPS modules, in addition to an A-PCP di-

domain, as well as lone A and PCP domains, thus also predicted to encode a molecule of

complex structure. The gene content of this gene cluster shared the highest overall homology

(17 %) to the calcium-dependent cyclic lipopetide antibiotic gene cluster identified in

S. coelicolor (A3)2. Additionally, the composition and arrangement of the genes shared 100

% sub-cluster homology with the clinically important glycopeptide antibiotic teicoplanin

isolated from Actinoplanes teichomyceticus. Due to the structural dissimilarities between DPO

and teicoplanin, this gene cluster was ruled out as the putative DPO biosynthetic cluster.

The secondary metabolite gene cluster spanning the region located from nucleotide 5343994-

5398013 (Appendix A) consisted of 2 A-PCP di-domains, 1 NRPS elongation module, as well

as 2 freestanding C domains and a freestanding PCP domain. The A domains within this gene

cluster were predicted to be specific for the activation of valine, aspartate and alanine, therefore

ruling out the formation of a heterocycle such as DPO.


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The secondary metabolite gene cluster spanning the region from nucleotide 5634984-5665006

(Appendix A) consisted of a nonlinear NRPS module which deviated from the classical C-A-

PCP domain organization and consisted of a lone A domain encoded by an acyl-CoA

synthetase, two lone C domains, a lone PCP domain and a lone TE domain. All of the genes

within this cluster shared homology to the congocidine biosynthetic gene cluster identified in

S. ambofaciens ATCC 23877T. Due to the fact that this cluster was significantly smaller than

any of the other secondary metabolite clusters encoding NRPSs and because the A domains

were predicted to be specific for the activation of aromatic amino acids, it was explored in

greater depth.

3.4.4 INVESTIGATION INTO THE PUTATIVE DPO GENE CLUSTER

The gene cluster spanning the region on the draft S. polyantibioticus SPRT genome from

positions 5634984-5665006 was preliminarily identified as the DPO biosynthetic gene cluster

based on the antiSMASH 3.0 analysis and due to the fact that the NRPS genes comprising this

cluster most closely resembled the gene architecture hypothesized to be involved in DPO

biosynthesis, in comparison to the remainder of the secondary metabolite clusters identified in

the genome. The genes in this cluster were further analysed with BLASTp to determine protein

homologies and conserved domains (Table 3.2).

The in silico analysis identified an atypical NRPS, consisting of a freestanding nonlinear

module and several single-domain proteins encoded by four genes, as the components of the

putative DPO biosynthetic cluster. Interestingly, the composition of the gene cluster and the

arrangement of the genes were most similar to the pyrrole-amide congocidine (also known as

netropsin) (Figure 3.2) biosynthetic gene cluster identified in S. ambofaciens ATCC 23877T,

as 100 % of the S. polyantibioticus SPRT genes shared homology to the genes within the

congocidine cluster. Congocidine biosynthesis is characterised by an NRPS that displays some

unusual features, namely that the A domain acts iteratively and the C domain uses a CoA-

activated substrate rather than a PCP-phosphopantetheinyl-activated substrate. Additionally,

the organization of the only complete NRPS module, A-PCP-C, differs from the canonical C-

A-PCP organization and the remaining NRPS-associated domains are freestanding (Juguet et

al., 2009).


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Figure 3.2 Outline of the chemical structure of congocidine.

Freestanding A and PCP domains, such as the A domain encoded by gene SPR_52860 and the

PCP encoded by SPR_53070, are normally found when a particular amino acid is modified

before its incorporation into the secondary metabolite, such as found in the biosynthesis of the

aminocoumarins and vancomycin (Juguet et al., 2009; Fischbach & Walsh, 2006).

Freestanding C domains, such as those encoded by SPR_52900 and SPR_53040, as well as

those involved in the biosynthesis of vibriobactin, are, however, far less frequent. The

condensation reactions catalysed by freestanding C domains generally necessitate a PCP-

tethered biosynthetic intermediate and a nucleophilic substrate free in solution (Juguet et al.,

2009; Keating et al., 2002), such as the ArCP-bound benzoyl intermediate proposed during

DPO biosynthesis.

There are 24 genes constituting the putative DPO biosynthetic cluster starting with SPR_52860

and ending at SPR_53090 (Figure 3.3). Table 3.2 presents an overview of the predicted

function of each of the products of the genes, as well as their proposed role in DPO

biosynthesis. Two of the genes, SPR_52870 and SPR_52880, are predicted to confer resistance

to DPO and one of the genes, SPR_52890, is predicted to encode a regulator for DPO

biosynthesis. Out of the remaining 21 genes, 5 genes, SPR_52900, SPR_53040, SPR_53060,


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SPR_53070 and SPR_53090, are predicted to encode NRPS-associated domains, while

another, SPR_52860, encodes an enzyme belonging to the AMP-binding superfamily of

proteins and highly resembles acyl-CoA synthetases. The role of the proteins encoded by the

remaining 15 genes cannot be easily inferred from the in silico analysis. Indeed, the presence

of 5 genes, SPR_52960 to SPR_53000, encoding proteins involved in sugar biosynthesis is

perplexing, as DPO does not contain a sugar moiety. It is possible that a glycosylated form of

DPO is synthesised by S. polyantibioticus SPRT, however, this putative glycosylated derivative

has not been isolated. It is also possible that the putative glycosyltransferase encoded by

SPR_52980 and the putative mannanase encoded by SPR_53010 are involved in a self-

resistance mechanism involving the inactivation of DPO by intracellular glycosylation and

extracellular reactivation by hydrolysis of the added sugar, similar to the type of mechanism

demonstrated in Streptomyces antibioticus (Juguet et al., 2009; Quirós et al., 1998).

The genes, cgc4, cgc5, cgc6 and cgc7, present in the congocidine biosynthetic pathway and

homologous to SPR_52920, SPR_52930, SPR_52940 and SPR_52950, respectively, were

characterized as having no involvement in the biosynthesis of congocidine (Lautru et al., 2012).

Similarly, it is possible that these genes play no part in DPO biosynthesis.

Although the putative DPO gene cluster closely resembles both the type and order of the genes

present in the congocidine biosynthetic cluster, there are a number of differences, namely: 1)

the mannanase encoded by SPR_53010 is absent in congocidine biosynthesis, 2) the TE domain

encoded by SPR_53090 is absent in congocidine biosynthesis, and 3) the A domains encoded

by SPR_52860 and SPR_53060 confer specificity towards different substrates than the A

domains involved in congocidine biosynthesis.

In light of this and due to the existence of transposases encoded by SPR_49500 and

SPR_57250, it is possible that S. polyantibioticus SPRT acquired the region between the genes

encoding these enzymes in the form of a transposable genetic element, via horizontal gene

transfer facilitated by the transposases. The G + C content of this region is 72.5 %, which is

slightly higher than the G + C content of the S. polyantibioticus SPRT draft genome (71.53 %),

thereby suggesting that the transposable genetic element may have been acquired from another

actinomycete, such as Streptomyces netropsis DSM 40093 or S. ambofaciens ATCC 23877T.

It also suggests that S. polyantibioticus SPRT has adapted the pathway for pyrrolamide

biosynthesis for the production of DPO.


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Table 3.2 Components of the putative DPO biosynthetic cluster and their proposed

function

Gene ID Size (aa)

GenBank accession number

Closest species match

Identity (%)

Putative function Proposed role in DPO biosynthesis

SPR_52860 518 AHF81557 Streptomyces netropsis DSM

40093

65 Acyl-CoA synthetase DPO assembly


40093

75 ABC transporter, ATP-binding protein

Resistance


40093

74 ABC transporter, transmembrane

protein

Resistance


40093

57 Two-component response regulator

Regulation


40093

62 NRPS, C domain Not involved

SPR_52910 479 CAJ88625 Streptomyces ambofaciens ATCC

23877

71 Aldehyde dehydrogenase

Unknown


40093

65 Nucleoside 2-deoxyribosyltransferas

e

Unknown


40093

73 Dihydroorotate dehydrogenase

Unknown


40093

79 Creatinine amidohydrolase

Unknown


40093

79 Hypothetical protein -hydrolase

Unknown


40093

75 Nucleotide sugar dehydrogenase

Unknown


40093

78 Nucleoside-diphosphate sugar

epimerase

Unknown


40093

72 Glycosyltransferase Unknown

SPR_52990 254 CAJ88617 Streptomyces ambofaciens ATCC

23877

73 Sugar nucleotidyl transferase

Unknown


40093

77 Nucleotide sugar aminotransferase

Unknown


40093

71 Mannanase Unknown

http://www.ncbi.nlm.nih.gov/protein/573026165?report=genbank&log$=prottop&blast_rank=2&RID=S7ST96GG01R

http://blast.ncbi.nlm.nih.gov/blast/Blast.cgi#alnHdr_117165072



http://www.ncbi.nlm.nih.gov/protein/573026160?report=genbank&log$=prottop&blast_rank=1&RID=S7UNZVGV01R

http://www.ncbi.nlm.nih.gov/protein/573026158?report=genbank&log$=prottop&blast_rank=1&RID=S7UYUPCC01R









123


40093

76 Amidohydrolase Unknown


40093

70 Methyltransferase Unknown

SPR_53040 450 AIS24860 Streptomyces netropsis DSM

40093

60 NRPS, C domain DPO assembly


40093

78 Alcohol dehydrogenase

Unknown

SPR_53060 1084

AHF81539 Streptomyces netropsis

DSM40093

60 NRPS, A-PCP-C DPO assembly

SPR_53070 124 ASI24864 Streptomyces netropsis

DSM40093

66 NRPS, PCP domain Not involved

SPR_53080 221 WP_037790144 Streptomyces sp.

Mg1

72 Hypothetical protein Not involved

SPR_53090 259 WP_030674398

Streptomyces sp. NRRL B-1347

79 TE domain DPO assembly

NRPS, nonribosomal peptide synthetase; C, condensation; A, adenylation; PCP, peptidyl carrier protein; TE,

thioesterase. Percentages of identity refer to deduced amino acid sequence comparisons.

http://www.ncbi.nlm.nih.gov/protein/664137791?report=genbank&log$=prottop&blast_rank=1&RID=S7G08EHU014

http://www.ncbi.nlm.nih.gov/protein/664137791?report=genbank&log$=prottop&blast_rank=1&RID=S7G08EHU014




124

Figure 3.3 Genetic organization of the putative DPO biosynthetic gene cluster.

Furthermore, in order to further characterize the individual NRPS domains contained within

the putative DPO biosynthetic cluster, known signature motifs and catalytic residues were

identified and assessed for integrity against a selection of reference proteins derived from the

CDD (Marchler-Bauer et al., 2011). These analyses are described in the following sections.

3.4.4.1 A DOMAIN SPECIFICITY

Prediction of the substrate specificity of the A domains encoded by SPR_52860 and

SPR_53060 was carried out using the NRPSpredictor2 (Röttig et al., 2011), the LSI algorithm

(Baranasic et al., 2013), NRPS/PKS predictor (Bachmann & Ravel, 2009), the Non-Ribosomal

Peptide Synthase Substrate Predictor (NRPSsp) (Prieto et al., 2012) and the Stachelhaus

specificity-conferring code (Stachelhaus et al., 1999) (Table 3.3). The A domain specificity

predictions were not conclusive as the web-based NRPS prediction services produced different


125

results for the A domains encoded by SPR_52860 and SPR_53060. However, the A domain

specificity results for the domains encoded by SPR_52860 and SPR_53060 were in agreement

with the prediction that the substrate would be aromatic i.e. tryptophan, phenylalanine and/or

2,3-dihydroxybenzoic acid.

The NRPSpredictor2 result for the query domain encoded by SPR_52860, based on the gross

physico-chemical properties, was that the substrate is hydrophobic and aliphatic, but with a

very low score of 0.190785. The result based on the gross physico-chemical properties for the

query domain encoded by SPR_53060, predicts that the substrate is hydrophilic with a slightly

higher, but still inconclusive score of 0.375341. On the basis of these highly questionable

predictions, it was not possible to infer the A domain specificity of the query domains encoded

by SPR_52860 and SPR_53060 using the NRPSpredictor2 output. Furthermore, Rausch et al.

(2005) commented that the NRPSpredictor2 server predicts aromatic substrates less reliably

due to the observed promiscuity of the A domains utilizing these substrates (Rausch et al.,

2005). Indeed, substrate promiscuity has been observed in Xenorhabdus nematophila where

two A domains that exhibit specificity for tryptophan in xenematide A biosynthesis can accept

either tryptophan or phenylalanine as substrates to produce a diverse family of products.

Markedly, this tryptophan/phenylalanine promiscuity is accommodated in the downstream

domains and results in a small family of cyclic depsipeptides (Crawford et al. 2011).

Instances of relaxed substrate specificity have also been observed in cyanobacterial NRPS A

domains, where structurally related amino acids such as valine, isoleucine and leucine are

located in equivalent positions of the final peptide products. These NRPS pathways produce

entire families of structurally related compounds all co-occurring in one specific isolate

(Christiansen et al., 2011).

Both of the A-domain specificity prediction results obtained from the LSI algorithm were based

on a LSI score of below 0.66, which is classified as an unreliable prediction (Baranasic et al.,

2013).

The A domain specificity prediction based on the profile Hidden Markov Model (pHMM)

approach developed by Prieto et al. (2012) and known as NRPSsp, resulted in both query

domains predicted to be specific for the activation of phenylalanine. However, the authenticity

of this prediction server was questioned by Khayatt et al. (2013) who claimed that the dataset


126

that the NRPSsp server is based on contains erroneous annotations and several sequences not

related to NRPSs.

The NRPS/PKS prediction server developed by Bachmann & Ravel (2009) could not identify

the A domain specificity for either query domain. The Stachelhaus specificity-conferring code

predicted the substrates 2,3-dihydroxybenzoic acid and tryptophan for the query domains

encoded by SPR_52860 and SPR_53060, respectively, with a score of 60 % in each case. In

comparison to the scores achieved by the other prediction servers/algorithms, these are the most

reliable. However, Rausch et al. (2005) noted that Stachelhaus predictions at less than a 70%

threshold are less reliable and lead to inconsistent predictions. In light of this statement and

the fact that tryptophan-and phenylalanine-specific domains are known to be interchangeable,

it is possible that the query domain, SPR_53060, displays a relaxed specificity and activates

phenylalanine (or 3-hydroxyphenylalanine) instead of tryptophan. Furthermore, it is possible

that the query domain, SPR_52860, also displays relaxed substrate specificity, allowing it to

activate benzoic acid rather than 2,3-dihydroxybenzoic acid.

Table 3.3 A domain specificity predictions

NRPSpredictor 2

(Röttig et al.,

2011)

LSI

(Baranasic et

al., 2013)

NRPS/PKS

(Bachmann &

Ravel, 2009)

NRPSsp

(Prieto et al.,

2012)

Stachelhaus

code

(Stachelhaus

et al., 1999)

SPR_52860 Hydrophobic-aliphatic

tryptophan NO HIT phenylalanine 2,3-dihydroxy-benzoic acid

SPR_53060 Hydrophilic tryptophan NO HIT phenylalanine tryptophan

3.4.4.2 CY DOMAINS

The NaPDos online tool did not identify any obvious Cy domains within the S. polyantibioticus

SPRT genome sequence. In light of this, a phylogenetic analysis was performed in order to

determine the evolutionary relatedness of all the annotated C domains within the S.

polyantibioticus SPRT genome in comparison to reference Cy domain sequences from the

Streptomyces virginiae NRRL B-1446T VirH sequence (GenBank accession number:


127

AB283030), S. coelicolor A3(2) putative non-ribosomal peptide synthetase sequence

(CAC17500), Streptomyces verticillatus strain ATCC 15003 BlmIV sequence (AAG02364),

Pseudomonas aeurginosa PA14 PchE sequence (AAD55800), Bacillus licheniformis ATCC

10716 BacA sequence (O68006), Sorangium cellulosum So ce90 EposP sequence (AAF26925)

and the Streptomyces flavoviridis ATCC 21892 Zbm sequence (EU670723).

The phylogenetic analysis, using the neighbour joining (NJ) (Figure 3.4) and maximum

likelihood (ML) (Figure 3.5) algorithms, resolved the putative C domains from

S. polyantibioticus SPRT and the reference Cy domain sequences into two distinct groups. The

first group consisted of 19 of the putative C domains found within the S. polyantibioticus SPRT

genome sequence, while the second group consisted of all of the reference Cy domains plus

the S. polyantibioticus SPRT C domains encoded by SPR_52900, SPR_53040, SPR_53060,

SPR_6230, SPR_6240 and SPR_6360. From the neighbour-joining phylogenetic analysis, it

can be inferred that the S. polyantibioticus SPRT genes in the second group are further sub-

divided into three clusters, wherein SPR_6230 was more closely related to the reference Cy

domains than SPR_6360, SPR_6240, SPR_53040, SPR_53060, and SPR_52900. Moreover,

SPR_6240 was more closely related to SPR_53040 and SPR_53060 than was SPR_6230, with

SPR_52900 being the least related to the reference Cy domains. However, the bootstrap support

for the association of SPR_6230, SPR_6240, SPR_6360, SPR_53040 and SPR_53060 with

known Cy domain sequences was very weak (<50%).

In contrast, the phylogenetic analysis using the ML algorithm resolved the S. polyantibioticus

SPRT genes in the second group into five clusters, wherein SPR_6240 was the most closely

related to the reference Cy domains, followed by SPR_53040, SPR_53060, SPR_6360,

SPR_52900 and SPR_6230. Similarly to the NJ tree, the bootstrap support for the association

of SPR_6230, SPR_6240, SPR_6360, SPR_52040 and SPR_53060 with known Cy domain

sequences was very weak (<50%).

Similarly, the phylogenetic analysis using the maximum parsimony (MP) (Figure 3.6)

algorithm, resolved the C domains from S. polyantibioticus SPRT and the reference Cy domain

sequences into two distinct groups. However, while the first, most distantly-related group

consisted of only S. polyantibioticus SPRT encoded C domains, the second group consisted of

the Cy reference domains, in addition to the S. polyantibioticus SPRT genes encoded by

SPR_6230, SPR_6240, SPR_6360, SPR_53060 and SPR_53040. This algorithm established


128

that SPR_6360 was most closely related to the reference Cy domains, followed by SPR_6240,

SPR_53060, SPR_53040 and SPR_6230. In contrast to the NJ and ML algorithms, SPR_52900

was not associated with the Cy domain reference sequences in this instance.

It is clear from the phylogenetic analyses that the S. polyantibioticus SPRT amino acid

sequences from SPR_6230, SPR_6240, SPR_6360, SPR_53060 and SPR_53040 were

consistently associated with the reference Cy domains, suggesting that SPR_6230, SPR_6240,

SPR_6360, SPR_53060 and SPR_53040 encode Cy domains, despite being annotated as C

domains. It has been reported that despite secondary structure predictions indicating a similar

overall fold for both Cy and C domains, there is weak primary sequence homology between

the two (Kelly et al., 2005; Keating et al., 2002). This has contributed to the lack of knowledge

regarding the catalytic mechanism of the Cy domains and only a detailed structural and

mutational analysis of the catalytic residues of the domains will help to elucidate the

mechanisms involved (Hur et al., 2012). Despite primary sequence differences, Figures 3.3-

3.5 show that C and Cy domains can be distinguished by phylogenetic analyses.

The phylogenetic analysis of the putative C and Cy domains prompted a comprehensive

investigation of the signature motifs and catalytic residues contained within the domains

encoded by SPR_53060, SPR_52900, SPR_53040, SPR_6230, SPR_6240 and SPR_6360, as

these domains shared the highest degree of evolutionary relatedness to the reference Cy

domains (Figure 3.7).

Heterocyclization domains replace C domains in NRPS modules that produce thiazoline or

oxazoline rings. In addition, the catalytic core motif, H-H-x-x-x-D-G, of regular C domains is

replaced by a D-x-x-x-x-D-x-x-S motif found in Cy domains; the two aspartate residues play

an essential part in both condensation and heterocyclization reactions (Keating et al., 2002).

An additional seven Cy domain signature motifs were described by Schwarzer et al. (2003), all

of which were analysed using a multiple sequence alignment with reference Cy domain

sequences from the S. virginiae NRRL B-1446T VirH sequence (GenBank accession number:

AB283030), S. coelicolor A3(2) putative non-ribosomal peptide synthetase sequence

(CAC17500), S. verticillatus strain ATCC 15003 BlmIV sequence (AAG02364),

Pseudomonas aeurginosa PA14 PchE sequence (AAD55800), Bacillus licheniformis ATCC

10716 BacA sequence (O68006), Sorangium cellulosum So ce90 EposP sequence (AAF26925)

and the Streptomyces flavoviridis ATCC21892 Zbm sequence (EU670723) (Figure 3.7).


129

The putative Cy domains encoded by SPR_53040, SPR_53060 and SPR_52900 shared a

35 %, 41 % and 24 % homology, respectively, to the eight NRPS Cy domain signature motifs.

By comparison, the two Cy domains encoded by the angN gene found in the NRPS module of

Vibrio anguillarum 775, revealed only 23 % and 19 % homology with 7 other characterised

Cy domains in a multiple sequence alignment (Di Lorenzo et al., 2008). Within the core motif

(D-x-x-x-x-D-x-x-S), SPR_52900 displayed neither of the essential catalytic aspartate residues

and was therefore concluded to be inactive. In contrast, SPR_6230 displayed both of the

critical catalytic aspartate residues, while SPR_6240 and SPR_6360 each displayed only the

second catalytic aspartate residue. Similarly, SPR_53040 and SPR_53060 each displayed only

one of the catalytic aspartate residues. However, SPR_53040 displayed the first catalytic

aspartate residue, while SPR_53060 displayed the second aspartate residue, suggesting the

possible complementation of the catalytic activity required in the formation of DPO.

Indeed, it has been demonstrated that the two different Cy domains found in the VibF NRPS

of the vibriobactin biosynthetic pathway perform either the role of the condensation reaction

or the role of heterocyclization. A mutation of the catalytic aspartate residue in one domain

resulted in lower heterocyclic product formation, whilst maintaining condensation activity. A

mutation in the second domain caused the opposite effect (Keating et al., 2002). However,

from the multiple sequence alignment alone, it cannot be determined whether the two domains,

SPR_53040 and SPR_53060, together provide the catalytic activity required for the formation

of DPO by S. polyantibioticus SPRT.


130

Figure 3.4 Unrooted phylogenetic tree obtained by the neighbour-joining method (Saitou & Nei, 1987) from an alignment of the amino acid sequences of S. polyantibioticus SPRT C domains and heterocyclization domain sequences from the S. virginiae NRRL B-1446T Vir sequence (S.virginiae cyc), S. coelicolor A3(2) putative non-ribosomal peptide synthetase sequence (S. coelicolor cyc), S. verticillatus strain ATCC 15003 BlmIV sequence (S.verticillus cyc), Pseudomonas aeurginosa PA14 PchE sequence (P.aeurginosa cyc), Bacillus licheniformis ATCC 10716 BacA sequence (B. licheniformis cyc), Sorangium cellulosum So ce90 EposP sequence (S. cellulosum cyc) and the Streptomyces flavoviridis ATCC21892 Zbm sequence (S.flavoridis cyc). The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches and the GenBank accession numbers are displayed in parenthesis. The analysis involved 32 amino acid sequences and all positions containing gaps and missing data were eliminated. Scale bar, 20 amino acid substitutions per 100 amino acids.


131

Figure 3.5 Unrooted phylogenetic tree obtained by the Maximum Likelihood method (Jones et al., 1992) based on the JTT matrix-based model for the amino acid sequences of S. polyantibioticus SPRT C domains and heterocyclization domain sequences from the S. virginiae NRRL B-1446T VirH sequence (S.virginiae cyc), S. coelicolor A3(2) putative non-ribosomal peptide synthetase sequence (S. coelicolor cyc), S. verticillatus strain ATCC 15003 BlmIV sequence (S.verticillus cyc), Pseudomonas aeurginosa PA14 PchE sequence (P.aeurginosa cyc), Bacillus licheniformis ATCC 10716 BacA sequence (B. licheniformis cyc), Sorangium cellulosum So ce90 EposP sequence (S. cellulosum cyc) and the Streptomyces flavoviridis ATCC21892 Zbm sequence (S.flavoridis cyc). The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches and the GenBank accession numbers are displayed in parenthesis. Initial tree(s) for the heuristic search were obtained automatically by applying Neighbor-Join and BioNJ algorithms to a matrix of pairwise distances estimated using a JTT model, and then selecting the topology with superior log likelihood value (Tamura et al., 2013). The analysis involved 32 amino acid sequences. All positions containing gaps and missing data were eliminated. Scale bar, 50 amino acid substitutions per 100 amino acids.


132

Figure 3.6 Unrooted phylogenetic tree obtained by the Maximum Parsimony (MP) method (Felsenstein, 1985) for the amino acid sequences of S. polyantibioticus SPRT C domains and heterocyclization domain sequences from the S. virginiae NRRL B-1446T VirH sequence (S.virginiae cyc), S. coelicolor A3(2) putative non-ribosomal peptide synthetase sequence (S. coelicolor cyc), S. verticillatus strain ATCC 15003 BlmIV sequence (S.verticillus cyc), Pseudomonas aeurginosa PA14 PchE sequence (P.aeurginosa cyc), Bacillus licheniformis ATCC 10716 BacA sequence (B. licheniformis cyc), Sorangium cellulosum So ce90 EposP sequence (S. cellulosum cyc) and the Streptomyces flavoviridis ATCC21892 Zbm sequence (S.flavoridis cyc). The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches and the GenBank accession numbers are displayed in parenthesis. The MP tree was obtained using the Subtree-Pruning-Regrafting (SPR) algorithm with search level 1 in which the initial trees were obtained by the random addition of sequences (10 replicates) (Nei & Kumar, 2000). The analysis involved 32 amino acid sequences. All positions containing gaps and missing data were eliminated.


133

Cyc motif 1 F P L T/S 2x Q x A Y 2x G R VirH-cyc L P L T (2x) Q S A Y (2x) G R NRPS-cyc F P L T (2x) Q A A Y (2x) G R blmIV-cyc F P L T (2x) Q R A Y (2x) G R BacA-cyc F P L T (2x) Q L A Y (2x) G R EposP-cyc F P L T (2x) Q E S Y (2x) G R PchE-cyc F E L S (2x) Q Q A Y (2x) G R Zbm-cyc F P L T (2x) Q Q A Y (2x) G R SPR_6230 A P P S (2x) Q E E H (2x) Q A SPR_6240 A P L S (2x) Q E E M (2x) N I SPR_6360 G P L S (2x) Q R R F (2x) A E SPR_53040 G P L S (2x) Q L G M (2x) L E SPR_53060 - P L T (2x) Q W R M (2x) H H SPR_52900 A S A T (2x) Q R Q M (2x) L I

Cyc motif 2 R H P/A/L G x Q Cy motif 3 D 4x D 2x S VirH-cyc H H R V H Q VirH-cyc D (4x) D (2x) S NRPS-cyc R H R I H Q NRPS-cyc D (4x) D (2x) S blmIV-cyc R H R V L P blmIV-cyc D (4x) D (2x) S BacA-cyc R H R V F E BacA-cyc D (4x) D (2x) S EposP-cyc R H R T L P EposP-cyc D (4x) D (2x) S PchE-cyc R H R F F D PchE-cyc D (4x) D (2x) S Zbm-cyc R H R I D A Zbm-cyc D (4x) D (2x) S SPR_6230 R H R F R T SPR_6230 D (4x) D (2x) S SPR_6240 R H R I A Y SPR_6240 H (4x) D (2x) S SPR_6360 R H R Y P W SPR_6360 H (4x) D (2x) S SPR_53040 R H R F T V SPR_53040 D (4x) W (2x) V SPR_53060 R H R L A T SPR_53060 H (4x) D (2x) S SPR_52900 R H E S L R SPR_52900 S (4x) A (2x) S

Cy motif 4 L P 2x P x L P L 3x P VirH-cyc L P (2x) P P L P D (3x) Q NRPS-cyc L P (2x) P E L P L (3x) A blmIV-cyc L P (2x) P G L P L (3x) P BacA-cyc F P (2x) P E L P L (3x) P EposP-cyc L P (2x) P T L P M (3x) P PchE-cyc L P (2x) P A L P L (3x) P Zbm-cyc L P (2x) P E L P F (3x) P SPR_6230 L S (2x) L L P Q A (3x) P SPR_6240 L A (2x) T G E V A (3x) P SPR_6360 A A (2x) P V L P T (3x) N SPR_53040 V A (2x) P E L T L (3x) T SPR_53060 A P (2x) T R L P T (3x) P SPR_52900 A P (2x) M F P G R (3x) G


134

Cy motif 5 T/S P/A 3x L/A/F 6x I/V/T L 2x W VirH-cyc P A 3x L 6x E L 2x T NRPS-cyc T P 3x L 6x T V 2x W blmIV-cyc T P 3x I 6x V L 2x W BacA-cyc T P 3x L 6x I L 2x W EposP-cyc T P 3x I 6x V I 2x W PchE-cyc T L 3x F 6x V L 2x W Zbm-cyc T P 3x L 6x I V 2x W SPR_6230 T L 3x L 6x A S 2x I SPR_6240 S P 3x L 6x A I 2x V SPR_6360 A T 3x C 6x G R 2x P SPR_53040 T L 3x L 6x V L 2x H SPR_53060 T P 3x I 6x V A 2x S SPR_52900 S T 3x L 6x L L 2x R

Cy motif 6 G/A D F T x L x L L VirH-cyc A D F T Q L A W V NRPS-cyc G D F T S L E L L blmIV-cyc G D F T T T T L L BacA-cyc G D F T S L M L L EposP-cyc G D F T S M V L L PchE-cyc A D F T T L L L L Zbm-cyc G D F T S L I P L SPR_6230 G W Y I N A A P I SPR_6240 G H L L N T R L T SPR_6360 V V D T A A D Q V SPR_53040 G L F V N M L P I SPR_53060 G L F T H T V P L SPR_52900 A N L H Q E V L T

Cy motif 7 P V V F T S x L VirH-cyc P V V F T R V P NRPS-cyc P V V F T S A L blmIV-cyc P V V F T S T L BacA-cyc P I V F T S V L EposP-cyc P V V L T S A L PchE-cyc P V V F A S N L Zbm-cyc P V V F T S N L SPR_6230 S Y L D F R P L SPR_6240 L S P E W E A Q SPR_6360 S S V R V R P P SPR_53040 I N V C V S F Q SPR_53060 Q M V F C H G A SPR_52900 T V V A S S D F


135

Cy motif 8 S/T Q/R T P Q V x L/I D 13x W D VirH-cyc S Q T A Q V A L D 13x W D NRPS-cyc T R T P Q V W L D 13x W D blmIV-cyc S Q T P Q V L L D 13x W D BacA-cyc T R T S Q V Y I D 13x W D EposP-cyc T Q T P Q L L L D 13x W D PchE-cyc S Q T P Q V W L D 13x W D Zbm-cyc - - - - - - - - - - - - SPR_6230 S G T G I D L F L 13x P D SPR_6240 S W R S F A V L W 13x R P SPR_6360 Q W R E D V M D R 13x A E SPR_53040 S P F D L D L G F 13x N P SPR_53060 A K F D V T V M V 13x Y D SPR_52900 C A E T A A L S P 13x L V

Figure 3.7 A multiple sequence alignment of the conserved signature motifs of the putative S. polyantibioticus SPRT Cy domains, encoded by SPR_6230, SPR_6240, SPR_6360, SPR_53040, SPR_53060 and SPR_52900, and reference Cy domain amino acid sequences taken from the S. virginiae NRRL B-1446T VirH sequence (VirH-cyc) (AB283030), S. coelicolor A3(2) putative non-ribosomal peptide synthetase sequence (NRPS-cyc) (CAC17500), S. verticillatus strain ATCC 15003 BlmIV sequence (blmIV-cyc) (AAG02364), Pseudomonas aeurginosa PA14 PchE sequence (PchE-cyc) (AAD55800), Bacillus licheniformis ATCC 10716 BacA sequence (BacA-cyc) (O68006), Sorangium cellulosum So ce90 EposP sequence (EposP-cyc) (AAF26925) and the Streptomyces flavoviridis ATCC21892 Zbm sequence (Zbm-cyc) (EU670723). Residues critical for the domain function are coloured green while other residues corresponding to the consensus motif are coloured yellow.

3.4.4.3 PCP DOMAINS

The peptidyl carrier protein enables the transfer of activated amino acids and elongation

intermediates between catalytic centres. The PCP domain is characterised by a conserved

serine residue, which accepts a phosphopantetheine moiety as a prosthetic group, thereby

converting the inactive apo-PCP to its active holo-form. A variant of the PCP has been

identified in the synthetases of siderophores and other aryl-capped non-ribosomal peptides for

the incorporation of aromatic carboxy acids, where aryl acids such as salicylate and 2,3-

dihydroxybenzoic acid are tethered on ArCPs (Crosa & Walsh, 2002). In particular,

freestanding A domains are known to activate aromatic carboxylic acids and transfer them to

aryl-carrier proteins (ArCP), which are used as starter substrates in, for example, quinoxaline

antibiotics (Crawford et al., 2011).


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Marahiel et al. (1997) identified the signature motif, L-G-G-(D/H)-S-L, in all PCP and ArCP

domains. The antiSMASH analysis of the draft S. polyantibioticus SPRT genome identified

two PCP domains in the putative DPO gene cluster (Table 3.2), which were examined in a

multiple sequence alignment with reference ArCP domains from Yersinia enterocolitica subsp.

enterocolitica 8081 (GenBank accession number: YE2617), Brucella melitensis bv. 1 str. 16M

(BMEII0079), Bacillus subtilis (BSU31970), Escherichia coli (P0ADI4), Pseudomonas

aeruginosa PA14 (AAD55800), Salmonella enterica subsp. enterica (STM0597) and

Streptomyces pyridomyceticus (AEF33099). The alignment revealed the presence of the

critical catalytic serine residue in the putative ArCP domain encoded by SPR_53060, and the

absence of this serine residue in the putative PCP domain encoded by SPR_53070 (Figure 3.8).

The signature motif is well conserved in the SPR_53060 domain and very poorly conserved in

the SPR_53070 domain, with the exception of the final leucine residue, suggesting the possible

inactivity/redundancy of the domain encoded by SPR_53070. Indeed, the essential serine

residue is replaced by an arginine residue, which would prevent the attachment of the

phosphopantetheine prosthetic group.

PCP motif L G G D/H S L Y.enterocolitica-ArCP A G L D S I B.melitensis-ArCP Y G L D S L B.subtilis-ArCp R G L D S V E.coli-ArCp Y G L D S V P.aeruginosa-ArCP C G L D S I S.enteric-ArCP Y G L D S V S.pyridomyceticus-ArCP L G L D S I SPR_53060 R G G D S L SPR_53070 Q A I G R L

Figure 3.8 A multiple sequence alignment of the conserved signature motifs of the putative S. polyantibioticus SPRT ArCP domain encoded by SPR_53060 and the PCP domain encoded by SPR_53070 with reference ArCP domains from Yersinia enterocolitica subsp. enterocolitica 8081 (Y.enterocolitica-ArCP), Brucella melitensis bv. 1 str. 16M (B.melitensis-ArCP), Bacillus subtilis (B.subtilis-ArCP), Escherichia Coli (E.coli-ArCP), Pseudomonas aeruginosa PA14 (P.aeruginosa-ArCP), Salmonella enterica subsp. enterica (S.enteric-ArCP)) and Streptomyces pyridomyceticus (S.pyridomyceticus-ArCP). Residues critical for the domain function are coloured green while other residues corresponding to the consensus motif are coloured yellow.


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Due to the fact that both PCP and ArCP domains share the same conserved signature motif, a

phylogenetic analysis was performed (Figure 3.9) in order to determine the evolutionary

relatedness of the putative ArCP domain encoded by SPR_53060 and the PCP domain encoded

by SPR_53070 to the reference ArCP domains used in the analysis of the conserved signature

motifs (Figure 3.8). The PCP domains from Streptomyces netropsis DSM 40846 (GenBank

accession number: AHF81539), Streptomyces sp. CNS615 (WP_037734274), Streptomyces

himastatinicus ATCC 53653 (WP_009720528), S.coelicolor A3(2) (NP_631722),

Streptomyces lividans 1326 (EOY52612) were added to the phylogenetic analysis.

The phylogenetic analysis, using the NJ, ML and MP algorithms, resolved the putative ArCP

and PCP domains from S. polyantibioticus SPRT and the reference sequences into two distinct

groups. The reference ArCP domains clustered together in all three trees (with very high

bootstrap support (98 %) in the NJ tree) and the reference PCP domains clustered together with

the amino acid sequences of SPR_53060 and SPR_53070. There was strong bootstrap support,

93 % and 67 %, respectively, for the association of SPR_53060 and SPR_53070 with known

PCP domain sequences.

This analysis indicated that the domain encoded by SPR_53060 is in fact a PCP domain and

not an ArCP, as originally suggested by the conserved signature motif analysis.


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Figure 3.9 Unrooted, neighbour joining tree (Saitou & Nei, 1987) obtained from an alignment of the amino

acid sequences of the putative S. polyantibioticus SPRT ArCP domain encoded by SPR_53060 and the PCP domain encoded by SPR_53070 with reference ArCP domains from Yersinia enterocolitica subsp. enterocolitica 8081 (Y.enterocolitica-ArCP), Brucella melitensis bv. 1 str. 16M (B.melitensis-ArCP), Bacillus subtilis (B.subtilis-ArCP), Escherichia Coli (E.coli-ArCP), Pseudomonas aeruginosa PA14 (P.aeruginosa-ArCP), Salmonella enterica subsp. enterica (S.enterica-ArCP)) and Streptomyces pyridomyceticus (S.pyridomyceticus-ArCP), in addition to PCP domains from Streptomyces netropsis DSM 40846 (S.netropsis PCP), Streptomyces sp. CNS615 (Streptomyces sp. CNS615 PCP), Streptomyces himastatinicus ATCC 53653 (S.himastatinicus PCP), S.coelicolor A3(2) (S.coelicolor PCP) and Streptomyces lividans 1326 (S.lividans PCP). The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches and the GenBank accession numbers are displayed in parenthesis. The evolutionary distances were computed using the Poisson correction method and are in the units of the number of amino acid substitutions per site (Zuckerkandl & Pauling, 1965). The analysis involved 14 amino acid sequences and all positions containing gaps and missing data were eliminated. Asterisks indicate clades that were conserved in neighbour-joining, maximum-likelihood and maximum-parsimony trees. Scale bar, 20 amino acid substitutions per 100 amino acids.


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3.4.4.4 OX DOMAINS

An Ox domain is required during DPO biosynthesis for the oxidation of the initial unstable

oxazoline ring to an oxazole ring, as postulated in Chapter 2 (section 2.2.1). Ox domains have

been identified as members of the McbC-like oxidoreductase superfamily and are normally

associated with heterocyclization modules (Marchler-Bauer et al., 2011).

A BLASTP search against the S. polyantibioticus SPRT draft genome, using well-characterised

Ox domain amino acid sequences from: Streptomyces hygroscopicus McbC-like

oxidoreductase (GenBank accession number: ACS50132), Streptomyces sp. NRRL WC-3773

NADH oxidase (WP_031005407), Streptomyces verticillus ATCC15003 peptide synthetase

(AAG02365), S. cellulosum epothilone biosynthetic cluster (AAF62881) and Angiococcus

disciformis tubulysin biosynthetic cluster (CAF05649), revealed the existence of putative Ox

domains within the genome encoded by the genes SPR_01300, SPR_37410, SPR_39290,

SPR_39400, SPR_44390, SPR_49120 and SPR_53180 amongst others. However, no Ox

domains were found within the putative DPO biosynthetic cluster (section 3.4.4). This suggests

that the oxidation activity required in DPO biosynthesis may be provided by an external

tailoring enzyme. Indeed, the in trans thiazoline to thiazole oxidase activity of the S.

cellulosum EpoB Ox domain was demonstrated by Schneider et al. (2003) who heterologously

expressed this domain in E. coli. Additionally, the mechanism of the oxidation process remains

unclear, but it does share a clear analogy to the oxidation of dihydroorotate to orotate observed

in pyrimidine biosynthesis, in which an FMN co-factor-mediated redox step is involved

(Schenider et al., 2003). In light of this, it is interesting to note that a homologue of the key

enzyme involved in this reaction, dihydroorotate dehydrogenase, is encoded by the gene

SPR_52930, identified as a member of the putative DPO biosynthetic pathway. Although DPO

is not a pyrimidine, both compounds are aromatic heterocycles and therefore the presence of a

homologue of dihydroorotate dehydrogenase within the putative DPO biosynthetic cluster may

indicate its involvement in the oxidation process required for DPO biosynthesis.

Lastly, in contrast to all other NRPS domains, whose relative position within a given module

is generally highly conserved, the location of the EpoB and BlmIII Ox domains from

S. cellulosum and Streptomyces verticillatus ATCC 15003, respectively, suggest that Ox

domains can be located either upstream or downstream of the PCP domains presenting

thiazolinyl-S-pantotheinyl chains for oxidation. This may be indicative of the fact that Ox-PCP


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and PCP-Ox pairs may be transferable to other Cy-containing modules in NRPS assembly

lines, thereby preserving the ability to direct the catalysis of thiazolinyl and oxazolinyl-S-

enzyme intermediates to heterocycle oxidation states (Schneider et al., 2003). A similar

atypical positioning of the Ox domain may also occur in the genes for DPO biosynthesis in

S. polyantibioticus SPRT.

3.4.4.5 TE DOMAIN

The gene SPR_53090 was identified by antiSMASH to encode a TE domain. These domains

share the same G-x-S-x-G motif, described by Schwarzer et al. (2003), as the acyltransferase

enzymes found in PKS systems that catalyse the transfer of acyl moieties between CoA and

ACP using a serine-histidine catalytic diad (Yadav et al., 2003).

A multiple sequence alignment of SPR_53090 with known TE domains from Bacillus and

Streptomyces species revealed the highly conserved G-x-S-x-G signature motif in SPR_53090

(Figure 3.10), thereby indicating that it is likely responsible for the thioesterase activity in the

proposed DPO biosynthetic gene cluster.

Te motif G x S x G B.cereus-Te G H S M G B.licheniformis-Te G H S M G S.coelicolor-Te G H S M G S.aureofaciens-Te G H S M G SPR_53090 G H S L G

Figure 3.10 A multiple sequence alignment of the conserved signature motif of the putative DPO TE domain from S. polyantibioticus SPRT and various TE reference sequences taken from S. coelicolor A3(2) (S.coelicolor-Te) (GenBank ccession number: NP_631726), S. aureofaciens (S.aureofaciens-Te) (YP_009060793), Bacillus cereus AH1134 (B.cereus-Te) (EDZ49042) and B. licheniformis IBL200 (B.licheniformis-Te) (AAU22005). Residues critical for the domain function are coloured green while other residues corresponding to the consensus motif are coloured yellow.


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3.4.4.6 GENES INVOLVED IN BENZOIC ACID BIOSYNTHESIS

In addition to identifying the NRPS-associated genes involved in DPO biosynthesis, the genes

for benzoic acid biosynthesis also need to be identified. Despite its common occurrence in

plant metabolites, benzoic acid biosynthesis is not common in bacteria (Moore et al., 2002).

However, the biosynthesis of benzoate as a starter unit in the biosynthesis of enterocin in

‘Streptomyces maritimus‘ strain DSM 41777T prompted a search of the draft S. polyantibioticus

SPRT genome for an orthologue of the encP gene, encoding the key enzyme, phenylalanine

ammonia-lyase. An encP homologue is not present in the putative DPO biosynthetic cluster,

or anywhere else in the S. polyantibioticus SPRT genome.

The annotation of the draft genome of S. polyantibioticus SPRT revealed the presence of an

enoyl-CoA hydratase, cinnamate-CoA ligase, and an acyl-CoA dehydrogenase encoded by

genes SPR_60140, SPR_60150 and SPR_60160, respectively. The enoyl-CoA hydratase and

cinnamate CoA ligase shared 25 % and 27 % homology, respectively, to the homologous

proteins found in the benzoate biosynthetic pathway identified in ‘S. maritimus‘ strain DSM

41777T.

Despite the fact that a PAL homologue was not identified in the S. polyantibioticus SPRT draft

genome, an alternative route to cinnamic acid was proposed whereby phenylalanine would be

catabolized to cinnamic acid via phenylpyruvate and phenyllactate (Figure 3.9). Indeed,

several catabolic pathways for L-phenylalanine have been reported in various organisms,

including Streptomyces setonii 75Vi2, which metabolises L-phenylalanine via phenylpyruvate

and phenyllactate (Pometto III & Crawford, 1985). Moreover, it has been reported that lactic

acid bacteria catabolize phenylalanine to phenylpyruvate via an aminotransferase, after which

phenylpyruvate is catabolized to either D- or L-phenyllactate via dehydrogenase activity (Mu

et al., 2012). It has also been demonstrated that a D-lactate dehydrogenase from Leuconostoc

mesenteroides can reduce phenylpyruvate to phenyllactate (Simon et al., 1989).

In light of these reports and the fact that a putative aminotransferase encoded by SPR_60250

and a putative D-lactate dehydrogenase encoded by SPR_60260 were clustered together with

the genes encoding the enoyl-CoA hydratase, cinnamate-CoA ligase, and an acyl-CoA

dehydrogenase mentioned above, it was decided to explore the possibility of these genes being

involved in the biosynthesis of benzoate and therefore DPO production, as functionally related


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genes are usually clustered in bacterial genomes (Kaneko et al., 2003). Therefore, the genes

encoding the cinnamate-CoA ligase and D-lactate dehydrogenase were identified as putative

external constituents of the DPO biosynthetic pathway. The investigation into their

involvement in the DPO biosynthetic pathway is explored in Chapter 4.

Figure 3.9 Proposed biosynthetic pathway for benzoyl-CoA production in S. polyantibioticus SPRT.

Lastly, the gene coding for the phenylacetate-coenzyme A ligase, paaK, which was identified

in the S. polyantibioticus SPRT genome via PCR amplification and sequencing (Chapter 2),

was identical to the sequence of the gene SPR_46390 obtained from the annotation of the draft

S. polyantibioticus SPRT genome. The antiSMASH 3.0 (Weber et al., 2015) analysis identified

the cluster that the paaK gene was located in as a PKS/NRPS hybrid encoding an antimycin-

type antibiotic. The composition of the gene cluster was most similar in gene content and gene

order to the antimycin biosynthetic gene cluster from Streptomyces blastmyceticus, as 100 %

of the S. polyantibioticus SPRT genes shared homology to genes within this cluster but, due to

the complicated structure of antimycin (PubChem ID: 14957) (Figure 3.10), it was deemed

unlikely that this cluster would be involved in DPO biosynthesis. However, further efforts to

characterize the involvement of paaK in the synthesis of DPO are described in Chapter 4.

http://pubchem.ncbi.nlm.nih.gov/compound/14957


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Figure 3.10 Outline of the S. polyantibioticus SPRT antimycin structure predicted by antiSMASH 3.0.


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3.5 CONCLUSION

The draft S. polyantibioticus SPRT genome sequence was obtained using a hybrid sequencing

approach, after which the sequence was annotated and secondary metabolite gene clusters were

identified using antiSMASH 3.0 analysis (Weber et al., 2015). The putative DPO biosynthetic

gene cluster was identified using a genome mining approach in which each of the six NRPS-

containing gene clusters was assessed for the likelihood of it being responsible for producing

DPO, based on the structure of DPO and the gene content of each gene cluster.

The putative DPO biosynthetic cluster shared a high degree of homology to the biosynthetic

gene cluster for the pyrrole-amide, congocidine, identified in S. ambofaciens ATCC 23877T.

The putative acyl-CoA synthetase encoded by SPR_52860, the A domain encoded by

SPR_53060, the putative Cy domain encoded by SPR_53040, the TE domain encoded by

SPR_53090, the cinnamate-CoA ligase encoded by SPR_60150 and the putative D-lactate

dehydrogenase encoded by SPR_60260 were identified as genes that would be disrupted in

order to determine their involvement in DPO biosynthesis. The development of a DNA

transformation method for the introduction of exogenous DNA into S. polyantibioticus SPRT

and subsequent gene disruption experiments are described in the following chapter.


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3.6 REFERENCE LIST Aigle, B., Lautru, S., Spiteller, D., Dickschat, J. S., Challis, G. L., Leblond, P. & Pernodet, J. L. (2014). Genome mining of Streptomyces ambofaciens. Journal of industrial microbiology & biotechnology, 41(2): 251-263. Bachmann, B.O. & Ravel, J. (2009). In Silico Prediction of Microbial Secondary Metabolic Pathways from DNA Sequence Data. Methods in Enzymology, 458: 181-217. Bachmann, B.O., Van Lanen, S.G. & Baltz, R.H. (2014). Journal of Industrial Microbiology and Biotechnology, 41: 175-184. Baltz, R., H. (2008). Renaissance in antibacterial discovery from actinomycetes. Current Opinion in Pharmacology. 8:557–563. Baranasic, D., Zucko, J., Diminic, J., Gacesa, R., Long, P.F., Cullum, J., Hranueli, D. & Starcevic, A. (2013). Predicting substrate specificity of adenylation domains of nonribosomal peptide synthetases and other protein properties by latent semantic indexing. Journal of Industrial Microbiology and Biotechnology, DOI 10.1007/s10295-013-1322-2. Bentley SD, Chater KF, Cerdeno-Tarraga AM, Challis GL, Thomson NR, James KD, Harris DE, Quail MA, Kieser H, Harper D, Bateman A, Brown S, Chandra G, Chen CW, Collins M, Cronin A, Fraser A, Goble A, Hidalgo J, Hornsby T, Howarth S, Huang CH, Kieser T, Larke L, Murphy L, Oliver K, O’Neil S, Rabbinowitsch E, Rajandream MA, Rutherford K, Rutter S, Seeger K, Saunders D, Sharp S, Squares R, Squares S, Taylor K, Warren T, Wietzorrek A, Woodward J, Barrell BG, Parkhill J. & Hopwood DA. (2002). Complete genome sequence of the model actinomycete Streptomyces coelicolor A3(2). Nature, 417(6885):141–147. Bérdy, J. (2012). Thoughts and facts about antibiotics: Where we are now and where we are heading. The Journal of Antibiotics, 65: 385-395. Boddy, C.N. (2014). Bioinformatics tools for genome mining of polyketide and non-ribosomal peptides. Journal of Industrial Microbiology and Biotechnology, 41: 443-450. Christiansen, G., Philmus, B., Hemscheidt, T. & Kurmayer, R. (2011). Genetic Variation of Adenylation Domains of the Anabaenopeptin Synthesis Operon and Evolution of Substrate Promiscuity. Journal of Bacteriology, 193(15): 3822–3831. Crawford, J.M., Portmann, C., Kontnik, R., Walsh, C.T. & Clardy, J. (2011). NRPS Substrate Promiscuity Diversifies the Xenematides. Organic Letters, 13(19): 5144-5147. Crosa, J.G. & Walsh, C.T. (2002). Genetics and Assembly Line Enzymology of Siderophore Biosynthesis in Bacteria. Microbiology and Molecular Biology Reviews, 66 (2): 223-249. Delcher, A.L, Bratke, K.A., Powers, E.C. & Salzberg, S.L. (2007). Identifying bacterial genes and endosymbiont DNA with Glimmer. Bioinformatics, 23: 673–679. Di Lorenzo, M., Stork, M., Naka, H., Tolmasky, M. E. & Crosa, J. H. (2008). Tandem heterocyclization domains in a nonribosomal peptide synthetase essential for siderophore biosynthesis in Vibrio anguillarum. Biometals, 21(6): 635-648.

http://mmbr.asm.org/search?author1=Jorge+H.+Crosa&sortspec=date&submit=Submit

http://mmbr.asm.org/search?author1=Christopher+T.+Walsh&sortspec=date&submit=Submit


146

Disz, T., Akhter, S., Cuevas, D., Olson, R., Overbeek, R., Vonstein, V., Stevens, R. & Edwards, R.A. (2010). Accessing the SEED genome databases via Web ser vices API: tools for programmers. BMC Bioinformatics, 11 (31): 1-11 Edgar, R.C. (2004). MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Research, 32(5): 1792-1797. Felsenstein J. (1985). Confidence limits on phylogenies: An approach using the bootstrap. Evolution, 39:783-791. Fischbach, M.A. & Walsh, C.T. (2006). Assembly-line enzymology for polyketide and nonribosomal peptide antibiotics: logic, machinery and mechanisms. Chemical Reviews, 106: 3468-3496. Glenn, T.C. (2011). Field guide to next-generation DNA sequencers. Molecular Ecology Resources, 11: 759–769. Harrison, J., & Studholme, D. J. (2014). Recently published Streptomyces genome sequences. Microbial biotechnology, 7(5): 373-380. Hur, G.H., Vickery, C.R. & Burkart, M.D. (2012). Explorations of catalytic domains in non-ribosomal peptide synthetase enzymology. Natural Products Reports, 29: 1074-1098. Ikeda, H., Shin-ya, K. & Omura, S. (2014). Genome mining of the Streptomyces avermitilis genome and development of genome-minimized hosts for heterologous expression of biosynthetic gene clusters. Journal of industrial microbiology & biotechnology, 41(2): 233-250. Jankowitsch, F., Schwarz, J., Rückert, C., Gust, B., Szczepanowski, R., Blom, J., Pelzer, S., Kalinowski, J. & Mack, M. (2012). Genome Sequence of the Bacterium Streptomyces davawensis JCM 4913 and Heterologous Production of the Unique Antibiotic Roseoflavin. Journal of Bacteriology, 192(24): 6818-6827. Jensen, PR, Chavarria KL, Fenical W, Moore BS, Ziemert N. (2014). Challenges and triumphs to genomics-based natural product discovery. Journal of Industrial Microbiology & Biotechnology. 41: 203-209. Jones, D.T., Taylor, W.R., Thornton, J.M. (1992). The rapid generation of mutation data matrices from protein sequences. Computer Applications in the Biosciences, 8: 275-282. Juguet, M., Lautru, S., Francou, F. X., Nezbedová, Š., Leblond, P., Gondry, M., Pernodet, J. L. (2009). An iterative nonribosomal peptide synthetase assembles the pyrrole-amide antibiotic congocidine in Streptomyces ambofaciens. Chemistry & biology, 16(4): 421-431. Kaneko, M., Hwang, E. I., Ohnishi, Y., Horinouchi, S. (2003). Heterologous production of flavanones in Escherichia coli: potential for combinatorial biosynthesis of flavonoids in bacteria. Journal of Industrial Microbiology and Biotechnology, 30(8): 456-461. Keating, T.A., Marshall, C.G., Walsh, C.T. & Keating, A.E. (2002). Excision of the Epothilone Synthetase B Cyclization Domain and Demonstration of in Trans Condensation/Cyclodehydration Activity. Nature Structural Biology, 9(7): 522-526. Kelly, W.L., Hillson, N.J. & Walsh, C.T. (2005). Excision of the Epothilone Synthetase B Cyclization Domain and Demonstration of in Trans Condensation/Cyclodehydration Activity. Biochemistry, 44: 13385-13393.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Jankowitsch%20F%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Schwarz%20J%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=R%26%23x000fc%3Bckert%20C%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Gust%20B%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Szczepanowski%20R%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Blom%20J%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Pelzer%20S%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Kalinowski%20J%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Mack%20M%5Bauth%5D

http://scrippsscholars.ucsd.edu/pjensen/content/challenges-and-triumphs-genomics-based-natural-product-discovery-1

http://scrippsscholars.ucsd.edu/pjensen/content/challenges-and-triumphs-genomics-based-natural-product-discovery-1


147

Khayatt, B. I., Overmars, L., Siezen, R. J. & Francke, C. (2013). Classification of the adenylation and acyl-transferase activity of NRPS and PKS systems using ensembles of substrate specific hidden Markov models. PloS one, 8(4): 2136-2140. Lagesen K, Hallin, P., Rødland, E.A., Staerfeldt, H.H., Rognes, T. & Ussery, D.W. (2007). RNAmmer: consistent and rapid annotation of ribosomal RNA genes. Nucleic Acids Research, 35: 3100–3108. Lautru, S., Song, L., Demange, L., Lombès, T., Galons, H., Challis, G. L. & Pernodet, J. L. (2012). A Sweet Origin for the Key Congocidine Precursor 4‐Acetamidopyrrole‐2‐carboxylate. Angewandte Chemie International Edition, 51(30): 7454-7458. Le Roes-Hill, M. & Meyers, P. R. (2009). Streptomyces polyantibioticus sp. nov., isolated from the banks of a river. International Journal of Systematic and Evolutionary Microbiology, 59: 1302–1309. Levene, M. J., Korlach, J., Turner, S. W., Foquet, M., Craighead, H. G. & Webb, W. W. (2003). Zero-mode waveguides for single-molecule analysis at high concentrations. Science, 299(5607): 682-686. Li, M. H., Ung, P. M., Zajkowski, J., Garneau-Tsodikova, S. & Sherman, D. H. (2009). Automated genome mining for natural products. BMC bioinformatics, 10(1),:185. Liu, L., Li, Y., Li, S., Hu, N., He, Y., Pong, R., Lin, D., Lu, L. & Law, M. (2012). Comparison of Next-Generation Sequencing Systems. Journal of Biomedicine and Biotechnology, 1: 1-11. Lodish, H., Berk, A., Zipursky, S.,L., Matsudaira, P., Baltimore, D. & Darnell, J. (2000). Molecular Cell Biology, 4th edition. New York: W. H. Freeman. Loman, N.J., Constantinidou, C., Chan, J.Z., Halachev, M., Sergeant, M., Penn, C.W., Robinson, E.R. & Pallen, M.J. (2012). High-throughput bacterial genome sequencing: an embarrassment of choice, a world of opportunity. Nature reviews, 10: 599-606. Lowe, T.M. & Eddy, S.R. (1997). tRNAscan-SE: a program for improved detection of transfer RNA genes in genomic sequence. Nucleic Acids Research. 25: 955–964 Marahiel, M.A. (1997). Protein templates for the biosynthesis of peptide antibiotics. Chemistry & Biology, 4(8): 561-567. Marchler-Bauer, A., Lu, S., Anderson, J.B., Chitsaz, F., Derbyshire, M.K., DeWeese-Scott, C., Fong, J.H., Geer, L.Y., Geer, R.C., Gonzales, N.R., Gwadz, M., Hurwitz, D.I., Jackson, J.D., Ke, Z., Lanczycki, Lu, F., Marchler, G.H., Mullokandov, M., Omelchencko, M.V., Robertson, C.L., Song, J.S., Thanki, N., Yamashita, R.A., Zhang, N., Zheng, C. & Bryant, S.H. (2011) . CDD: a Conserved Domain Database for the functional annotation of proteins. Nucleic Acids Research, 39: 225–229. Mardis, E.R. (2013). Next-Generation Sequencing Platforms. Annual Review of Analytical Chemistry, 6: 287–303. Margulies, M., Egholm, M., Altman, W.E., Attiya, S., Bader, J.S., Bemben, L.A., Berka, J., Braverman, M.S., Chen, Y., Chen, Z., Dewell, S.B., Du, L., Fierro, J.M., Gomes, X.V., Godwin, B.C. & He, W. (2005). Genome sequencing in microfabricated high-density picolitre reactors, Nature, 437: 376–380. Medema, M. H., Blin, K., Cimermancic, P., de Jager, V., Zakrzewski, P., Fischbach, M. A. & Breitling, R. (2011). antiSMASH: rapid identification, annotation and analysis of secondary metabolite biosynthesis gene clusters in bacterial and fungal genome sequences. Nucleic acids research, 39(2): W339-W346.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Hallin%20P%5BAuthor%5D&cauthor=true&cauthor_uid=17452365

http://www.ncbi.nlm.nih.gov/pubmed/?term=R%C3%B8dland%20EA%5BAuthor%5D&cauthor=true&cauthor_uid=17452365

http://www.ncbi.nlm.nih.gov/pubmed/?term=Staerfeldt%20HH%5BAuthor%5D&cauthor=true&cauthor_uid=17452365

http://www.ncbi.nlm.nih.gov/pubmed/?term=Rognes%20T%5BAuthor%5D&cauthor=true&cauthor_uid=17452365

http://www.ncbi.nlm.nih.gov/pubmed/?term=Ussery%20DW%5BAuthor%5D&cauthor=true&cauthor_uid=17452365

http://www.whfreeman.com/


148

Metzker, M.L. (2011). Sequencing technologies – the next generation. Nature Reviews, 11: 31-46. Moore, B. S., Hertweck, C., Hopke, J. N., Izumikawa, M., Kalaitzis, J. A., Nilsen, G. & Noel, J. P. (2002). Plant-like biosynthetic pathways in bacteria: from benzoic acid to chalcone 1. Journal of natural products, 65(12): 1956-1962. Morozova, M.A., & Marra, M.A. (2008). Applications of next-generation sequencing technologies in functional genomics. Genomics, 92: 255-264. Mu, W., Yu, S., Zhu, L., Zhang, T. & Jiang, B. (2012). Recent research on 3-phenyllactic acid, a broad-spectrum antimicrobial compound. Applied microbiology and biotechnology, 95(5): 1155-1163. Nei M., & Kumar S. (2000). Molecular Evolution and Phylogenetics. Oxford University Press, New York. Nett, M., Ikeda, H. & Moore, B., S. (2009). Genomic basis for natural product biosynthetic diversity in the actinomycetes. Natural Product Reports. 26: 1362–1384. Niedringhaus, T.P., Milanova, D., Kerby, M.B., Snyder, M.P. & Barron, A.E. (2011). Landscape of Next-Generation Sequencing Technologies. Analytical Chemistry, 15: 4327-4341. Overbeek, R., Olson, R., Pusch, G.D., Olsen, G.J., Davis, J.J., Disz, T., Edwards, R.A., Gerdes, S., Parrello, B., Shukla, M., Vonstein, V., Wattam, A.R., Xia, F. & Stevens, R. (2014). The SEED and the Rapid Annotation of microbial genomes using Subsystems Technology (RAST). Nucleic Acids Research, 42: D206–D214.

Pohle, S., Appelt, C., Roux, M., Fiedler, H.P. & Süssmuth, R.D. (2011). Biosynthetic gene cluster of the non-ribosomally synthesized cyclodepsipeptide skyllamycin: deciphering unprecedented ways of unusual hydroxylation reactions. Journal of the American Chemical Society, 133(16): 6194-205.

Pometto III, A.L., & Crawford, D.L. (1985). L-Phenylalanine and L-tyrosine catabolism by selected Streptomyces species. Applied Environmental Microbiology, 49(3): 727-729. Prieto, C., García-Estrada, C., Lorenzana, D., Martín, J. F. (2012). NRPSsp: non-ribosomal peptide synthase substrate predictor. Bioinformatics, 28(3): 426-427. Quail, M.A., Smith, M., Coupland, P., Otto, T.D., Harris, S.R., Connor, T.R., Bertoni, A., Swerdlow, H.P., & Gu, Y. (2012). A tale of three next generation sequencing platforms: comparison of Ion Torrent, Pacific Biosciences and Illumina MiSeq sequencers. BMC Genomics, 13: 341-346. Quirós, L. M., Aguirrezabalaga, I., Olano, C., Méndez, C. & Salas, J. A. (1998). Two glycosyltransferases and a glycosidase are involved in oleandomycin modification during its biosynthesis by Streptomyces antibioticus. Molecular microbiology, 28(6): 1177-1185. Rausch, C. Weber, T., Kohlbacher, O., Wohlleben, W. & Huson, D.H. (2005). Specificity prediction of adenylation domains in nonribosomal peptide synthetases (NRPS) using transductive support vector machines (TSVMs). Nucleic Acids Research, 33: 5799-808. Roberts, R.J., Carneiro, M.O. & Schatz, M.C. (2013). The advantages of SMRT sequencing. Genome Biology, 14: 405-410.

Röttig, M., Medema, M.H., Blin, K., Weber, T., Rausch, C. & Kohlbacher, O. (2011). NRPSpredictor2 – a web server for predicting NRPS adenylation domain specificity. Nucleic Acids Research, 1-6.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Pohle%20S%5BAuthor%5D&cauthor=true&cauthor_uid=21456593

http://www.ncbi.nlm.nih.gov/pubmed/?term=Appelt%20C%5BAuthor%5D&cauthor=true&cauthor_uid=21456593

http://www.ncbi.nlm.nih.gov/pubmed/?term=Roux%20M%5BAuthor%5D&cauthor=true&cauthor_uid=21456593

http://www.ncbi.nlm.nih.gov/pubmed/?term=Fiedler%20HP%5BAuthor%5D&cauthor=true&cauthor_uid=21456593

http://www.ncbi.nlm.nih.gov/pubmed/?term=S%C3%BCssmuth%20RD%5BAuthor%5D&cauthor=true&cauthor_uid=21456593



149

Saitou, N. & Nei, M. (1987). The neighbor-joining method: a new method for reconstructing phylogenetic trees. Molecular Biology and Evolution 4, 406 – 425. Schadt, E.E., Turner, S. & Kasarskis, A. (2010). A window into third-generation sequencing. Human Molecular Genetics, 19(2): R227–R240 Schneider, T.L., Shen, B. & Walsh, C.T. (2003). Oxidase Domains in Epothilone and Bleomycin Biosynthesis: Thiazoline to Thiazole Oxidation during Chain Elongation. Biochemistry, 42: 9722-9730 Schwarzer, D., Finking, R. & Marahiel, M.A. (2003). Nonribosomal peptides: from genes to products. Natural Product Reports, 20: 275-287. Shendure, J., Porreca, G.J, Reppas, N.B, Lin, X., McCutcheon, J.P., Rosenbaum, A.M., Wang, M.D., Zhang, K., Mitra, R.D. & Church, G.M. (2005). Accurate multiplex polony sequencing of an evolved bacterial genome, Science, 309: 1728–1732. Simon, E. S., Plante, R. & Whitesides, G. M. (1989). D-lactate dehydrogenase. Applied biochemistry and biotechnology, 22(2): 169-179. Siqueira, J.F., Fouad, A.F. & Rocas, I.N. (2012). Pyrosequencing as a tool for better understanding of human microbiomes. Journal of Oral Microbiology, 4: 1-15 Stachelhaus, T., Mootz, H.D, & Marahiel, M.A. (1999). The specificity-conferring code of adenylation domains in nonribosomal peptide synthetases. Chemistry & Biology, 6: 493-505. Steinbock, L.J., & Radenovic, A. (2015). The emergence of nanopores in next-generation sequencing. Nanotechnology, 26(7): 074003. Takahashi, K., & Nei, M. (2000). Efficiencies of fast algorithms of phylogenetic inference under the criteria of maximum parsimony, minimum evolution, and maximum likelihood when a large number of sequences are used. Molecular Biology and Evolution, 17(8): 1251-1258. Tamura K., Stecher G., Peterson D., Filipski A. & Kumar S. (2013). MEGA6: Molecular Evolutionary Genetics Analysis version 6.0. Molecular Biology and Evolution, 30: 2725-2729. Tatusov, R.L., Koonin, E.V., Lipman, D.J. (1997). A genomic perspective on protein families. Science, 278: 631–637. Tawflik, D.S. & Griffiths, A.D. (1998). Man-made cell-like compartments for molecular evolution, Nature Biotechnology, 16: 652–656. Udwary, D.W., Zeigler, L., Asolkar, R.N., Singan, V., Lapidus, A., Fenical, W., Jensen, P.R. & Moore, B.S. (2007). Genome sequencing reveals complex secondary metabolome in the marine actinomycete Salinispora tropica. Proceedings of the National Academy of Sciences USA, 104(25): 10376–10381 Weber, T., Blin, K., Duddela, S., Krug, D., Kim, H.U., Bruccoleri, R., Lee, S.Y., Fischbacj, M.A., Muller, R., Wohlleben, W., Breitling, R., Takano, E., & Medema, M.H. (2015). antiSMASH 3.0 — a comprehensive resource for the genome mining of biosynthetic gene clusters. Nucleic Acids Research, doi: 10.1093/nar/gkv437. Yadav, G., Gokhale, R. S. & Mohanty, D. (2003). Computational Approach for Prediction of Domain Organization and Substrate Specificity of Modular Polyketide Synthases. Journal of Molecular Biology, 328: 335–363.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Porreca%20GJ%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Reppas%20NB%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Lin%20X%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=McCutcheon%20JP%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Rosenbaum%20AM%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Wang%20MD%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Zhang%20K%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Mitra%20RD%5BAuthor%5D&cauthor=true&cauthor_uid=16081699

http://www.ncbi.nlm.nih.gov/pubmed/?term=Church%20GM%5BAuthor%5D&cauthor=true&cauthor_uid=16081699


150

Zhu, P. & Craighead, H.G. (2012). Zero-Mode Waveguides for Single-Molecule Analysis. Annual Review of Biophysics, 41: 269–93 Ziemert, N., Podell, S., Penn, K., Badger, J.H., Allen, E. & Jensen, P.R. (2012). The Natural Product Domain Seeker NaPDoS: A Phylogeny Based Bioinformatic Tool to Classify Secondary Metabolite Gene Diversity. PLoS One, 7(3): 34064-34068. Zuckerkandl, E. & Pauling L. (1965). Evolutionary divergence and convergence in proteins. Edited in Evolving Genes and Proteins by V. Bryson and H.J. Vogel, pp. 97-166. Academic Press, New York.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0034064

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CHAPTER 4

DEVELOPMENT OF A

TRANSFORMATION PROTOCOL

FOR STREPTOMYCES

POLYANTIBIOTICUS SPRT AND

GENE DISRUPTION EXPERIMENTS

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CHAPTER 4

DEVELOPMENT OF A TRANSFORMATION PROTOCOL

FOR STREPTOMYCES POLYANTIBIOTICUS SPRT AND GENE

DISRUPTION EXPERIMENTS 4.1 Abstract ...................................................................................................................... 154

4.2 Introduction ................................................................................................................ 156

4.3 Materials and Methods ............................................................................................... 163

4.3.1 Bacterial strains and plasmids ........................................................................ 163

4.3.2 Media and culture conditions ......................................................................... 164

4.3.3 Primer design ................................................................................................. 170

4.3.4 PCR protocols ................................................................................................ 172

4.3.4.1 Amplification of genes for cloning into plasmid vectors....... 172

4.3.4.2 Colony PCR ........................................................................... 173

4.3.5 Cloning and restriction endonuclease digestions ........................................... 173

4.3.6 Determination of the antibiotic susceptibility of S. polyantibioticus SPRT ... 176

4.3.7 Knockout construction by gene disruption experiments ................................ 176

4.3.7.1 Conjugation ............................................................................ 176

4.3.7.1.1 Transformation of plasmid DNA into E. coli

ET12567/pUZ8002 .................................................... 176

4.3.7.1.2 Conjugation between E. coli ET12567/pUZ8002 and

E. coli JM109 ............................................................. 177

4.3.7.1.3 Intergeneric conjugation between E. coli and

S. polyantibioticus SPRT ............................................ 177

4.3.7.1.4 Confirmation of single crossover exconjugants by PCR

amplification .............................................................. 179

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4.3.7.2 Electroporation ....................................................................... 180

4.3.7.2.1 Preparation of plasmid DNA for electroporation ....... 180

4.3.7.2.2 Electroporation ........................................................... 180

4.3.7.3 Protoplast transformation ....................................................... 183

4.3.7.3.1 Preparation of protoplasts .......................................... 183

4.3.7.3.2 Protoplast transformation ........................................... 184

4.3.8 Fermentation and isolation of DPO ............................................................... 184

4.3.9 High performance liquid chromatography (HPLC) ....................................... 186

4.3.10 Thin layer chromatography (TLC) bioautography analysis ........................... 187

4.4 Results and Discussion .............................................................................................. 188

4.4.1 Determination of the antibiotic susceptibility of S. polyantibioticus SPRT ... 188

4.4.2 The development of an optimized transformation protocol for

S. polyantibioticus SPRT ................................................................................ 188

4.4.2.1 Electroporation and protoplast transformation ...................... 188

4.4.2.2 Intergeneric conjugation ........................................................ 192

4.4.3 Gene disruption using the optimized intergeneric conjugation method ........ 196

4.4.4 Isolation of DPO from S. polyantibioticus SPRT and confirmation of its

activity against M. aurum A+ ........................................................................ 202

4.4.5 TLC bioautography analysis to determine the putative involvement of the

target genes in DPO biosynthesis .................................................................. 204

4.5 Conclusion ................................................................................................................. 210

4.6 Reference list ............................................................................................................. 211

Chapter 4 – Development of a transformation protocol for S. polyantibioticus SPRT and gene disruption experiments

154

CHAPTER 4

DEVELOPMENT OF A TRANSFORMATION PROTOCOL

FOR STREPTOMYCES POLYANTIBIOTICUS SPRT AND GENE

DISRUPTION EXPERIMENTS

4.1 ABSTRACT

In order to identify the genes involved in DPO biosynthesis, a DNA transformation protocol

was required for the introduction of plasmid DNA into S. polyantibioticus SPRT, so that

specific genes could be disrupted to establish whether their products are involved in the

biosynthesis of DPO. Although there are several published transformation protocols for the

introduction of DNA into streptomycetes, there is no method that is generally applicable to all

species. Due to the fact that S. polyantibioticus SPRT is a novel antibiotic-producing

actinobacterium, it was necessary to develop a unique DNA transformation method.

In this study, the classical methods of electroporation and protoplast transformation of plasmid

DNA proved unsuccessful in the transformation of S. polyantibioticus SPRT. However, an

optimised method of intergeneric conjugation using the methylation-deficient E. coli

ET12567/pUZ8002 strain allowed the transfer plasmid DNA into S. polyantibioticus SPRT with

a conjugation frequency of 8.3 x 10-6 exconjugants per 1 x 107 donor E. coli cells, thereby

providing a platform for the gene disruption experiments.

Subsequently, the genes identified from the S. polyantibioticus SPRT genome sequence

(Chapter 3) as being putatively involved in the biosynthesis of DPO were individually cloned

into the suicide vector, pOJ260, transformed into S. polyantibioticus SPRT by means of mating

with E. coli ET12567/pUZ8002 and insertionally activated via homologous recombination in

the recipient strain. The genes that were disrupted were: the A domain encoded by gene


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SPR_53060, the putative Cy domain encoded by gene SPR_53040, the acyl-coA synthetase

encoded by gene SPR_52860, the cinnamate-CoA ligase encoded by gene SPR_60150, the

putative D-lactate dehydrogenase encoded by gene SPR_60250, the thioesterase encoded by

gene SPR_53090 and a selection of the A domains identified in Chapter 2.

The method for isolating DPO was carried out on each of the mutant strains, S. polyantibioticus

∆AD2, S. polyantibioticus ∆A18, S. polyantibioticus ∆A16, S. polyantibioticus ∆A28, S.

polyantibioticus ∆A7, S. polyantibioticus ∆A99, S. polyantibioticus ∆PAAK, S.

polyantibioticus ∆CYC, S. polyantibioticus ∆LAC, S. polyantibioticus ∆ACY, S.

polyantibioticus ∆CIN and S. polyantibioticus ∆THI, and the extracts were assayed for activity

against M. aurum A+. The absence of activity against M. aurum A+ in the extracts from strains

S. polyantibioticus ∆A99, S. polyantibioticus ∆CYC and S. polyantibioticus ∆ACY suggested

the involvement of these genes in the biosynthesis of DPO.


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4.2 INTRODUCTION

Streptomycetes are well known for their ability to produce commercially useful secondary

metabolites with a variety of biological activities (Hopwood, 1989). In order to discover novel

biochemical pathways used in the production of these important compounds, or to enhance or

modify their production, it is necessary to manipulate the producing strains by genetic

engineering techniques. This requires transformation of exogenous DNA into the producing

strains and subsequent gene disruption experiments (Mazy-Servais et al., 1997).

Due to the fact that streptomycetes are not naturally competent for the uptake of exogenous

plasmid DNA and because a general system for competence induced by cold shock and calcium

treatment, such as that developed for E. coli, has not yet been developed for Streptomyces, it

has hampered progress in Streptomyces strain manipulation (Marcone et al., 2010; Kieser et

al., 2000). The work by Okanishi et al. (1974) on the preparation, regeneration and transfection

of protoplasts in Streptomyces spp. led to the discovery that plasmid DNA could be transformed

into protoplasts at a very high frequency in the presence of polyethylene glycol (PEG; Bibb et

al., 1978). Even though this method, which was subsequently modified and adapted, is still

widely used in the transformation of Streptomyces species, it became apparent after limited

success in species such as Streptomyces fradiae (Matshushima and Baltz, 1985), that no method

exists which is equally efficient for all Streptomyces species and strains. Each transformation

method therefore requires the optimization of each step for each individual strain (Mazy-

Servais et al., 1997).

The reason for the different response to protoplast transformation from taxonomically related

species may be linked to the variation in the composition and density of the bacterial cell wall.

Indeed, variation in the peptidoglycan structure in response to environmental conditions, aging,

and maturation in order to adapt to changing conditions may explain the intraspecific variability

in the susceptibility to cell wall digestion (Marcone et al., 2010; Vollmer, 2008). Another

serious limitation to this method is the occurrence of restriction-modification (R-M) systems,

which are widespread in streptomycetes. R-M systems are vital components of prokaryotic

defence mechanisms against invading foreign DNA, such as phage genomes, that can decrease

transformation frequencies or make transformants undetectable, depending on the origin of the

DNA being introduced (Vasu & Nagaraja, 2013; MacNeil, 1988). The R-M systems generally


157

consist of two different enzymatic activities: a restriction endonuclease (REase) and a

methyltransferase (MTase). The REase is able to recognize and cleave foreign DNA sequences

at specific sites, whereas the MTase activity ensures differentiation between self and non-self

DNA by transfer of methyl groups to specific DNA sequences within the host’s genome (Figure

4.1) (Vasu & Nagaraja, 2013). However, methyl-specific restriction systems have also been

described (Raleigh & Wilson, 1986; Lacks & Greenberg, 1977), whereby foreign methyl-

modified DNA is restricted and the host strain does not modify its own DNA. Indeed,

Streptomyces avermitilis NRRL 8165 contains a unique restriction system that restricts plasmid

DNA containing N6-methyladenine or 5-methylcytosine. Additionally, S. coelicolor A3(2) is

known to strongly restrict DNA from modification-proficient E. coli strains such as E. coli

K12, but readily accepts it when it originates from methylation-deficient strains (Kieser et al.,

2000; Flett et al., 1997; Kieser & Hopwood, 1991). Consequently, for the purpose of

transforming exogenous DNA into S. coelicolor A3(2), it is possible to thwart the R-M system

by isolating plasmid DNA from the methylation-deficient E. coli ET12567 strain (Kieser et al.,

2000). Generally, it is also possible to limit the restriction barrier by subjecting protoplasts to

heat treatment prior to transformation which serves to inactivate the restriction enzymes

(Hussain & Ritchie, 1991; Bailey & Winstanley, 1986).

Even though PEG-mediated transformation of protoplasts has allowed for the rapid

development of gene cloning systems in various Streptomyces species such as S. lividans 66,

S. rimosus R6 and S. coelicolor A3(2) amongst others, transformation of fragile protoplasts is

tedious and frequently not reproducible, and therefore many strains remain recalcitrant to

transformation (Pigac & Schrempf, 1995).

An alternative method to the use of chemicals in assisting the uptake of DNA by bacterial cells

is electroporation, which involves the application of a brief, high voltage electrical pulse to a

suspension of cells and DNA that results in the formation of transient membrane pores and

subsequent uptake of DNA by the cells (Pigac & Schrempf, 1995; Shigekawa & Dower, 1988).

Several Streptomyces species, such as Streptomyces parvulus IMET 41380 (Mazy-Servais et

al., 1997), Streptomyces vinaceus NCIB 8852 (Macy-Servais et al., 1997), S. lividans ATCC

1326 (Tyurin et al., 1995) and S. virginiae ATCC 13161 (Tyurin et al., 1995), have been

successfully transformed using electroporation. Due to the fact that electroporation avoids the

need to optimise conditions for protoplast preparation and regeneration, it is less tedious and


158

time consuming than protoplast transformation and has been reported to be particularly useful

in transforming previously “untransformable” strains (Pigac & Schempf, 1995). However,

conditions for electroporation have also been described as being strain-specific (Kieser et al.,

2000).

Figure 4.1 Illustration depicting R-M systems in their role as a defence mechanism in prokaryotes. R-M

systems are able to identify the methylation status of invading foreign DNA, as methylated

sequences are recognised as “self”, while any recognition sequences that lack methylation are

identified as “non-self” and cleaved by a REase. This is due to the fact that “self” DNA is

methylated at its appropriate recognition sites by a cognate MTase belonging to the specific R-

M system (Vasu & Nagaraja, 2013).

In recent years, there has been considerable interest in the use of intergeneric conjugation,

which evades restriction barriers, as a means of transferring plasmid DNA into actinomycetes.

This method allows for the construction and manipulation of recombinant plasmids in a host

such as E. coli, which is used to transfer the genetic material into the required recipient via

horizontal gene transmission (Giebelhaus et al., 1996). Conjugal DNA transfer is a highly

conserved mechanism that is generally mediated by plasmids which encode many critical

transfer-related functions (Mazodier & Davies, 1991). The first plasmid-mediated transfer to


159

be described involved the E. coli F plasmid, which has served as the model for nearly all

subsequently described conjugative plasmids from both Gram-negative and Gram-positive

bacteria (Lederberg and Tatum, 1946). Briefly, the plasmid DNA molecule is

endonucleolytically cleaved on a single strand by a plasmid-encoded relaxase protein, which

leads to the formation of a DNA-protein complex known as a relaxosome (Lanka & Wilkins,

1995). The cleaved strand is then transferred from the donor to the recipient cell via a bridge-

like structure known as a pilus (which connects the two cells). After conjugation, the donor

and recipient both contain the plasmid, which allows the recipient to serve as a donor in future

matings (Willetts & Wilkins, 1984).

In contrast to this conserved mechanism of conjugation witnessed throughout most of the

bacterial domain, conjugative plasmids of Streptomyces origin employ a different mode of

DNA transfer (Grohmann et al., 2003). The conjugative elements and transfer functions

present in Streptomyces plasmids are unique and encode fewer transfer functions compared to

plasmids from other genera. Indeed, in comparison to the approximately 25 functions required

by the E. coli F plasmid to mobilize DNA, the S. lividans plasmid pIJ101 only requires a 70

kDa membrane-associated product of the tra gene and the cis-acting locus of transfer (clt) to

mediate plasmid transfer (Grohmann et al., 2003). Moreover, the major transfer proteins of

conjugative Streptomyces plasmids are homologous to proteins which mobilize double-

stranded DNA in processes such as sporulation and cell division, instead of sharing similarity

with relaxases (Begg et al., 1995; Wu et al., 1995; Hopwood & Kieser, 1993). Additionally,

the conjugative transfer of Streptomyces plasmids has been shown to occur via a double-

stranded intermediate. Due to the fact that the Streptomyces conjugative system is unique,

there has been considerable interest in elucidating the manner in which streptomycetes mediate

plasmid transfer via conjugation (Grohmann et al., 2003; Possoz et al., 2001).

It was initially assumed that the transfer of plasmids by conjugation was confined to closely

related bacterial species or genera until Trieu-Cuot et al. (1987) dispelled this misconception

by demonstrating conjugation between Gram-negative E. coli and various Gram-positive

bacteria, which included Streptococcus lactis, Bacillus thuringiensis, S. aureus and

Enterococcus faecalis, amongst others. The shuttle plasmid used in the study, pAT187,

contained the origin of replication for E. coli and a broad-host range origin of replication for

Gram-positive bacteria. The transfer of the plasmid was contingent on the origin of transfer


160

(oriT) of the incompatability group P (IncP) broad-host range E. coli plasmid RK2 acting in

cis and the transfer gene (tra) functions of the IncPα E. coli plasmid RP4 supplied in trans

(Gormley & Davies, 1991; Mazodier et al., 1989). Since then, additional studies with similarly

constructed shuttle plasmids have shown that conjugative transfer between phylogenetically

unrelated microorganisms is possible (Gormley & Davies, 1991).

The first protocol for the intergeneric transfer of plasmids between E. coli and Streptomyces

spp. was reported by Mazodier et al. (1989). The success of this transfer was dependent on the

presence of a 760 bp, cis-acting, oriT-containing fragment from the plasmid RK2 and on the

conjugative functions, such as the Tra2 core of plasmid RP4, which encodes the DNA transport

apparatus important for pilus formation, supplied in trans by the E. coli donor strain. The same

method has been used successfully with several Streptomyces species such as S. fradiae, S.

ambofaciens, S. lividans and S. coelicolor (Bierman et al., 1992) and other actinomycetes such

as Amycolatopsis (Stegmann et al., 2001), Actinoplanes (Heinzelmann et al., 2003) and

Saccharopolyspora (Matshushima et al., 1994). Importantly, the conjugative functions of

plasmid RP4 and the RK2 derivative, pUZ8002, were used to mobilize the resident plasmids

in these studies (Paranthaman & Dharmalingam, 2003). It was also demonstrated that the

major biochemical events during the intergeneric conjugal transfer occurred at the oriT, which

included the formation of a relaxosome, nicking of the closed circular dsDNA molecule and

transfer of the ssDNA intermediate from donor to recipient (Grohmann et al., 2003; Frost et

al., 1994).

Numerous cloning vectors for the conjugative transfer from E. coli to Streptomyces spp. have

been constructed, most notably by Bierman et al. (1992), who reported the construction of

plasmid and cosmid vectors that function in Streptomyces spp. due to features that allow for:

a) integration via homologous recombination between the cloned DNA fragment within the

vector and the Streptomyces chromosome (e.g. pOJ260 and pKC1132), b) autonomous

replication (e.g. pOJ446 and pKC1139) and c) site-specific integration via the bacteriophage

ΦC31 attachment site (e.g. pSET152 and pKC1163) (Kieser et al., 2000). All of these vectors

contain the 760 bp oriT fragment from plasmid RK2 and E. coli replication functions from

pUC, P15A or P1, which allow the plasmids to serve as cloning vectors for construction to

occur in an E. coli host. The recombinant plasmids can then be transferred to the desired

Streptomyces strain. Plasmids such as pOJ260 and pKC1132 were designed to be unable to


161

replicate in Streptomyces spp. and are therefore most useful for gene disruption experiments,

whereas plasmids such as pOJ446 and the recently designed pJN100 (Nikodinovic & Priestley,

2006), contain replication functions for Streptomyces spp. and therefore can exist as

autonomous, multicopy plasmids that are useful for complementation studies (Bierman et al.,

1992).

The use of intergeneric conjugation as a means of transforming DNA into streptomycetes has

been extensively utilized due to the simplicity of performing the method in comparison to

developing separate procedures for protoplast preparation and regeneration. Additionally,

restriction barriers such as R-M systems are by-passed or have a drastically reduced effect

when ssDNA is transferred into the recipient (Flett et al., 1997; Matshushima et al., 1994).

This is due to the fact that the majority of REases require dsDNA for the recognition and

cleavage of foreign DNA (Vasu & Nagaraja, 2013). In addition, the use of E. coli shuttle

vectors that contain oriT allow site-specific or insert-directed chromosomal integration that is

extremely useful for targeted gene disruption (Kieser et al., 2000).

In summary, electroporation and protoplast transformation methods are widely used for

introducing plasmid DNA into streptomycetes, but due to their low efficiency, intergeneric

conjugation has provided an alternative means. It has been reported that optimal conditions

for different strains may vary and therefore a defined procedure for each strain must be

established to enable a high conjugation efficiency. Furthermore, conjugation with

streptomycete mycelial fragments has proven to provide higher numbers of recombinants than

conjugation performed with freshly germinated spores (Kieser et al., 2000; Matshushima et al.,

1994).

The development of an efficient transformation method for the introduction of plasmid DNA

into a specific strain of Streptomyces allows for the targeted manipulation of biosynthetic

pathways in order to characterize individual genes and their functions. This is performed

experimentally via the disruption of target genes using the method of homologous

recombination. In this method, a DNA fragment internal to the target gene is inserted into a

plasmid vector, which integrates into the chromosome of the recipient Streptomyces strain by

a single or double homologous crossover, depending on whether a selectable marker is

contained within the DNA fragment carrying all or part of the target gene. A single crossover


162

results in an integrated copy of the plasmid vector, which is flanked on either side by two

mutant alleles of the target gene i.e. one truncated at the 5' end and the other truncated at the 3'

end. A double crossover results in a mutant allele that replaces the chromosomal copy of the

target gene via two crossovers that cannot revert and is therefore more stable than a single

crossover mutant (Keiser et al., 2000).


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4.3.1 BACTERIAL STRAINS AND PLASMIDS

All Streptomyces and E. coli strains and plasmids that were used and constructed in this study

are listed in Table 4.1. The common conjugative donor strain E. coli S17-1, which carries an

integrated derivative of IncP-group plasmid RP4 encoding all of the required plasmid

mobilization functions, was used as a donor strain for intergeneric conjugation. E. coli DH5α

was used as a general host for all standard cloning procedures. E. coli JM109 was used as a

recipient strain in conjugation with the methylation deficient E. coli ET12567 (provided by Dr

P. Whitney Swain III, Promiliad Biopharma Inc., USA). E. coli ET12567 contains the ‘driver’

plasmid pUZ8002 (derived from RK2) and was also used as the donor strain for intergeneric

conjugation. Plasmid pUZ8002 carries the plasmid RK2 transfer functions necessary for

intergeneric conjugation. Plasmid pJN100 (Figure 4.2) (provided by Dr. P. Whitney Swain III,

Promiliad Biopharma Inc., USA) (GenBank accession number: DQ309424) (Nikodinovic &

Priestley, 2006) is a high copy number E. coli-Streptomyces shuttle vector derived from

plasmid RK2 and was used for the optimization of the intergeneric conjugation method

between the different E. coli donor strains and S. polyantibioticus SPRT, as well as the

complementation experiments in S. polyantibioticus SPRT.

Plasmid pOJ260 (Figure 4.3) (provided by Dr Bohdan Ostash, Department of Genetics and

Biotechnology, Ivan Franko National University of L'viv, L'viv, Ukraine) (GenBank accession

number: GU270843) is a non-replicating, integrative E. coli-Streptomyces shuttle vector

derived from the conjugative broad host range plasmid RK2, which was used to perform gene

disruption experiments by chromosomal integration via single crossover homologous

recombination in S. polyantibioticus SPRT. Plasmid pOJ260 does not replicate in Streptomyces

and can therefore be used as a suicide vector for gene disruption and replacement (Kieser et

al., 2000).

Plasmid pJNHYG is a derivative of pJN100 carrying a hygromycin resistance cassette. This

derivative was created by first performing a restriction endonuclease digestion of pORI101

(Figure 4.4) (GenBank accession number: EF216315) (Bourn et al., 2007) using NotI to release

a 2.44 kb fragment containing the entire hygromycin resistance cassette. Concomitantly, the

plasmid pJN100 was subjected to a restriction endonuclease digestion with NotI. The 2.44 kb


164

hygromycin resistance cassette was ligated into the NotI site of the restriction endonuclease

digested pJN100 using the Rapid DNA Ligation Kit (Thermo Scientific) (14 h at 4 °C)

according to the manufacturer’s instructions to generate the 8.9 kb pJNHYG plasmid. The T4

DNA ligase was inactivated at 80 °C for 20 min before transformation into E. coli DH5α. The

plasmid was isolated using a NucleoSpin Plasmid Isolation Kit (Machery Nagel, Germany)

according to the manufacturer’s instructions.

All of the other plasmids utilized in this study are derivatives of pOJ260 and pJN100 carrying

the PCR-amplified target genes used in the gene disruption experiments (section 4.3.7). S.

polyantibioticus SPRT was isolated by Dr Paul Meyers. S. coelicolor A3(2) (NRRL B-16638)

was obtained from the culture collection of the Agricultural Research Service, United States

Department of Agriculture (NRRL) (Peoria, Illinois, USA).

4.3.2 MEDIA AND CULTURE CONDITIONS

All Streptomyces strains used in this study were grown on ISP4 agar (10 g soluble starch, 1 g

K2HPO4, 1 g MgSO4, 2 g (NH4)2SO4, 1 g CaCO3, 1 mg FeSO4, 1 mg MgCl2, 1 mg ZnSO4, 18

g bacteriological agar per litre of dH20, pH 7.2), (Shirling & Gottlieb, 1966) at 30 °C for 7 days

in order for sporulation to occur, after which the spores were scraped off the surface of the agar

using a sterile inoculating loop and stored in 20 % glycerol at -20 °C until needed. Liquid SMC

medium (10 g glucose, 4 g yeast extract, 4 g peptone, 4 g K2HPO4, 2 g KH2PO4, 0.5 g MgSO4

per litre of dH20, pH 7.0) (Zhang et al., 1992) containing 10.3 % sucrose, ISP2 (YEME)

medium (10 g malt extract, 4 g glucose, 4 g yeast extract per litre of dH20, pH 7.3) (Shirling &

Gottlieb, 1966), Luria-Bertani broth (LB) (10 g tryptone, 5 g yeast extract, 5 g NaCl, per litre

of dH20) (Sambrook et al., 1989) and V medium (2.4 g soluble starch, 10 g glucose, 3 g meat

extract, 5 g yeast extract, 5 g tryptose per litre of dH20, pH 7.2) (Marcone et al., 2010) were

used to culture S. polyantibioticus SPRT for the collection of mycelium for intergeneric

conjugation experiments. CRM (10 g glucose, 100.3 g sucrose, 10 g MgCl2.6H20, 15 g tryptic

soy broth (TSB), 5 g yeast extract per litre of dH20, pH 7.2), tryptic soy broth (TSB)

supplemented with 0.24 mM threonine and 1 % glycine and YEME supplemented with 34 %

sucrose and 0.5 % glycine were used to culture S. polyantibioticus SPRT for electroporation of

mycelia. Solid agar media used for the cultivation of S. polyantibioticus SPRT and S. coelicolor

A3(2) exconjugants were mannitol soya (MS) medium (20 g mannitol, 20 g soya flour, 20 g


165

bacteriological agar per litre of tap water, pH 7.0), Middlebrook 7H9, YEME and ISP4 all

containing 10 or 20 mM MgCl2. Electroporated mycelia were plated on TSB agar or R2YE

agar (103 g sucrose, 0.25 g K2SO4, 10.12 g MgCl2.6H2O, 10 g glucose, 0.1 g casamino acids,

KH2PO4, 10 ml 0.5 % KH2PO4, 80 ml 3.68 % CaCl2.2H2O, 15 ml 20 % L-proline, 100 ml 5.73

% TES buffer, 2 ml trace elements solution (40 mg ZnCl2, 200 mg FeCl3.6H2O, 10 mg

CuCl2.2H2O, 10 mg MnCl2.4H2O, 10 mg Na2B4O7.10H2O, 10 mg (NH)4Mo7O24.4H2O per litre

of dH2O), 0.5 ml 1 N NaOH, 40 ml 10 % yeast extract per litre of dH20, pH 7.2). Finally,

hypertonic V medium was used to cultivate S. polyantibioticus SPRT for preparing protoplasts,

while R2YE or VMSO.1 (2.4 g soluble starch, 0.1 g glucose, 0.3 g meat extract, 0.5 g yeast

extract, 0.5 g tryptose, 3.5 g L-proline, 4 g bacteriological agar per litre of dH20, pH 7.2) media

were used for the regeneration of protoplasts. LB broth supplemented with antibiotics (50

µg/ml apramycin, 34 µg/ml chloramphenicol and 50 µg/ml kanamycin, as required) was used

for the cultivation of all E. coli strains.

Table 4.1 Strains and plasmids used in this study

Strain/plasmid Genotype/characteristics Reference

Strains

S. polyantibioticus

SPRT Wild type This study

∆AD2 SPRT derivative carrying an integrated copy of pOJAD2; aprR This study

∆A16 SPRT derivative carrying an integrated copy of pOJA16; aprR This study




∆PAAK SPRT derivative carrying an integrated copy of pOJPAAK; aprR This study


∆CYC SPRT derivative carrying an integrated copy of pOJCYC; aprR This study

∆ACY SPRT derivative carrying an integrated copy of pOJACY; aprR This study

∆LAC SPRT derivative carrying an integrated copy of pOJLAC; aprR This study

∆CIN SPRT derivative carrying an integrated copy of pOJCIN; aprR This study

∆THI SPRT derivative carrying an integrated copy of pOJTHI; aprR This study

PJNACY ∆ACY derivative complemented with pJNACY; aprR This study


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S.coelicolor

A3(2) Wild type NRRL

E. coli

ET12567 F- dam13::Tn9 dcm6 hsdM hsdR zjj202::Tn10 recF143 galK2

galT22 ara14 lacY1 xyl5 leuB6 thi1 tonA31 rpsL136 hisG4 tsx78

mtl1 glnV44

MacNeil et al.

(1992)

DH5α F- deoR endA1 recA1 relA1 gyrA96 hsdR17(rk-, mk+) supE44 thi-

1 phoA Δ(lacZYA-argF)U169 Φ80lacZΔM15 λ-

Bioline (UK)

S17-1 recA pro hsdR RP4-2-Tc::Mu-Km::Tn7 Simon et al.

(1983)

dam- dcm- F- dam-13:Tn9(CamR) dcm-6 ara-14 hisG4 leuB6 thi-1 lacY1

galK2 galT22 glnV44 hsdR2 xylA5 mtl-1 rpsL 136(StrR) rtbD1

tonA31 tsx78 mcrA mcrB1

Bioline (UK)

JM109 endA1, recA1, gyrA96, thi, hsdR17 (rk–, mk

+), relA1, supE44,

Δ(lac-proAB)

Yanisch-Perron

et al. (1985)

Plasmids

pGEM®-T Easy 3015 bp vector with 3’ - T overhangs, designed for cloning PCR

products; AmpR oriT lacZ

Promega

(USA)

pGEMAD-2 pGEM®-T Easy vector harbouring the AD2 PCR product This study

pGEMA-7 pGEM®-T Easy vector harbouring the A7 PCR product This study




pGEM-PAAK pGEM®-T Easy vector harbouring the paaK PCR product This study


pGEM-CYC pGEM®-T Easy vector harbouring the CYC PCR product This study

pGEM-ACY pGEM®-T Easy vector harbouring the ACY PCR product This study

pGEM-LAC pGEM®-T Easy vector harbouring the LAC PCR product This study

pGEM-CIN pGEM®-T Easy vector harbouring the CIN PCR product This study

pGEM-THI pGEM®-T Easy vector harbouring the THI PCR product This study

pJN100 6460 bp E. coli-Streptomyces shuttle vector derived from RK2; aprR

oriT snpA repColE1 reppIJ101

Nikodinovic &

Priestley,

(2006)

pOJ260 3469 bp non-replicating integrative E. coli-Streptomyces shuttle

vector derived from pKC787; aprR reppuc oriT lacZ

Bierman et al.

(1992)


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pOJAD2 720 bp PstI/SacII fragment of pGEMAD-2 inserted into the

PstI/SacII sites of pOJ260

This study

pOJA18 670 bp PstI/SacII fragment of pGEMA-18 inserted into the


This study



This study



This study



This study

pOJPAAK 700 bp PstI/SacII fragment of pGEM-PAAK inserted into the


This study

pOJA99 719 bp EcoRI fragment of pGEMA-99 inserted into the EcoRI site

of pOJ260

This study

pOJCYC 980 EcoRI fragment of pGEM-CYC inserted into the EcoRI site of

pOJ260

This study

pOJACY 921 bp EcoRI fragment of pGEM-ACY inserted into the EcoRI site

of pOJ260

This study

pOJLAC 608 bp PstI/SacII fragment of pGEM-LAC inserted into the


This study

pOJCIN 649 bp PstI/SacII fragment of pGEM-CIN inserted into the


This study

pOJTHI 473 bp PstI/SacII fragment of pGEM-THI inserted into the


This study

pJNACY 1557 bp EcoRI fragment of pGEM-ACY inserted into the EcoRI

site of pOJ260

This study

pUZ8002 Non-transmissable oriT-mobilizing RK2 derivative; dam dcm hsdS

Strr Telr Clmr Kmr

Paget et al.

(1999)

pJNHYG Derivative of pJN100 carrying a 2.44 kb hygromycin resistance

casette; aprR hygR oriT snpA repColE1 reppIJ101

This study

pORI101 5316 bp Mycobacterium-E. coli shuttle vector derived from

pAL5000; hygR Ori2 OriM reppMB1 reppAL5000 lacZ

Bourn et al.

(2007)


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Figure 4.2 Plasmid map of the E. coli-Streptomyces shuttle expression vector, pJN100, indicating the

position of selected restriction endonuclease sites (multiple sites for the same enzyme are shown

in red).. The red arrow represents an apramycin resistance cassette, a selectable marker in both

hosts. The grey arrow represents an oriTRK2 insertion that allows intergeneric conjugation

between E. coli and Streptomyces. The orange arrow represents the origin of replication of

plasmid pIJ101, which allows for replication to take place in the Streptomyces host, while the

purple arrow represents the origin of replication of plasmid ColE1, which allows for replication

to take place in the E. coli host. The blue arrow indicates the presence of the snpR gene, the

product of which activates the snpA promoter, for use in protein expression studies. The position

of a multiple cloning region (showing only the restriction sites relevant to this study) is indicated

as MCS (Nikodinovic & Priestley, 2006).


169

Figure 4.3 Plasmid map of the non-replicating integrative E. coli-Streptomyces shuttle vector, pOJ260,

indicating the position of selected restriction endonuclease sites (multiple sites for the same

enzyme represented by red text). The red arrow represents an apramycin resistance cassette, a

selectable marker in both hosts. The grey arrow represents an oriTRK2 insertion that allows

intergeneric conjugation between E. coli and Streptomyces, while the orange arrow represents

the origin of replication of plasmid pUC18, which allows for replication to take place in the

E. coli host. The green arrow represents the α-peptide coding region of the E. coli lacZ gene,

encoding the enzyme β-galactosidase, which also includes restriction sites conveniently

arranged as a multiple cloning region (Bierman et al., 1992).


170

Figure 4.4 Plasmid map of the mycobacterial shuttle vector, pORI101. The NotI restriction sites used in a

restriction endonuclease digestion to generate a 2.44 kb fragment containing the hygromycin

resistance gene, hygA, are depicted in red text. The mycobacterial replicon genes are

represented by RepA and RepB. The mycobacterial origin of replication is represented by OriM

(Bourn et al., 2007).

4.3.3 PRIMER DESIGN

PCR primers were designed for the amplification of the following genes based on the S.

polyantibioticus SPRT genome sequence (Chapter 3): the putative Cy domain (CYC) encoded

by gene SPR_53040, the A domain (AD99) encoded by gene SPR_53060, the acyl-CoA

synthetase (ACY) encoded by gene SPR_52860, the cinnamate CoA ligase (CIN) encoded by


171

gene SPR_60150, the putative D-lactate dehydrogenase (LAC) encoded by gene SPR_60250

and the thioesterase (THI) encoded by gene SPR_53090. The primer sequences and their

respective amplification product sizes are shown in Table 4.2.

Additionally, the primer set, ACYORF_F/ACYORF_R, was designed to amplify the full open

reading frame of the acyl-CoA synthetase (gene SPR_52860) and incorporated the ClaI

restriction enzyme recognition sequence at the 5' end of the ACYORF_F primer sequence and

the HindIII restriction enzyme recognition sequence at the 5' end of the ACYORF_R primer

sequence, in order to achieve the in-frame cloning of this gene into plasmid pJN100.

Table 4.2 Oligonucleotide primers designed in this study

Primer Name Primer Sequence (5'→3')

Expected product size for primer

pair ADFWD GTACACCTCGGGATCCACC

719 bp ADREV TCGCCCGTGCGGTACATGC

CYCFWD CGTGGTCGACGGAGCTCC 980 bp

CYCREV GGTGTAGAAGCCGAGATCG

THIF TATGCGTGCGTTCTTCACCG 473 bp

THIR AAGGTGCATTCGAGATAGGG

CINF CCCAGTACGACCTCTCCTCC 649 bp

CINR CGGCGGATCTTCTTGTACGG

LACF ACTTCGACCTGCTGAGTACG 608 bp

LACR CAGGAACTCCGCCTTGTACG

ACYF CTGTGGGAGCTCATCGACC 921 bp

ACYR CTCGGTGCTTCCGTAGACC

ACYORF_F ATTATAATCGATGCCCTCGACCACTGAATCCG 1557 bp

ACYORF_R GATAATAAGCTTTCAGGCCGTGTCGTCCCGGTGC

POJFWD GCTGCAAGGCGATTAAGTTGG Variable

POJREV CAGGCTTTACACTTTATGCTTCC “Variable” denotes that the expected product size changes with each different target gene being amplified

due to the fact that a different target gene specific primer is used in conjunction with either POJFWD or

POJREV (section 4.3.7.1.4)


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4.3.4 PCR PROTOCOLS

All PCR amplifications were performed using a Techne TC512 Thermal Cycler fitted with a

heated lid and gradient sample block.

4.3.4.1 AMPLIFICATION OF GENES FOR CLONING INTO PLASMID

VECTORS

Amplification of the A domain in gene SPR_53060 and the putative Cy domain in gene

SPR_53040 were performed using the ADFWD/ADREV and CYCFWD/CYCREV primer

sets, respectively. The cycling conditions used for the amplification of both domains were as

follows: initial denaturation at 98 oC for 1 min, followed by 35 cycles of denaturation at 98 oC

for 10 s, annealing at 55 oC for 30 s and elongation at 72 oC for 2 min, with a final elongation

at 72 oC for 10 min. PCR reactions consisted of: 100 ng of DNA, 1 U Phusion High-Fidelity

DNA polymerase (Thermo Fisher Scientific, USA), 0.5 μM of each primer, 0.2 mM of each

dNTP, 1 x Phusion HF buffer and 4 % (v/v) glycerol in a total volume of 50 μl.

Amplification of sections of the cinnamate CoA ligase (gene SPR_60150), the putative D-

lactate dehydrogenase (gene SPR_60250), the thioesterase (gene SPR_53090) and the acyl-

CoA synthetase (gene SPR_52860) were performed using the CINF/CINR, LACF/LACR,

THIF/THIR, ACYF/ACYR and ACYORF_F/ACYORF_R primer sets, respectively. The

cycling conditions used for the amplification of these genes were similar to those used for the

amplification with the ADFWD/ADREV and CYCFWD/CYCREV primer sets, except that the

annealing temperature was 51 oC for the THIF/THIR primer set, 53 oC for the ACYF/ACYR

primer set, 56 oC for the CINF/CINR and LACF/LACR primer sets and 60 oC for the

ACYORF_F/ACYORF_R primer set. PCR reactions were set up as described for the

amplification of the A and Cy domains mentioned above, with the exception of the glycerol

concentration, which was 2 % (v/v) for amplification using the CINF/CINR, LACF/LACR,

THIF/THIR and ACYF/ACYR primer sets and 8 % (v/v) for the ACYORF_F/ACYORF_R

primer set.


173

All PCR amplification products were resolved by electrophoresis alongside a λ-PstI molecular

marker on 0.8 % agarose gels containing 0.8 μg/ml ethidium bromide in order to analyse

amplicon size and assess primer specificity. The products were visualized using a long

wavelength UV light box (Bio-Rad Gel Doc EQ-system™, Bio-Rad Laboratories Inc., USA).

4.3.4.2 COLONY PCR

A colony PCR protocol was used to confirm the presence and correct size of the amplification

product in transformants harbouring recombinant constructs. The PCR cycling conditions for

the amplification of these inserts was as follows: initial denaturation at 95 oC for 5 min,

followed by 35 cycles of denaturation at 95 oC for 30 s, annealing at 60 oC for 90 s and

elongation at 72 oC for 60 s, with a final elongation at 72 oC for 10 min. PCR reactions consisted

of: a toothpick-tip size amount of cell mass from a transformant colony, 2 U SuperThem Taq

polymerase (JMR Holdings, USA), 0.5 μM of each primer, M13F and M13R (Table 2.1), 0.8

mM of each dNTP and 3 mM MgCl2 in a total volume of 20 μl.

All PCR amplification products were resolved by agarose gel electrophoresis alongside a λ-PstI

molecular marker on 0.8 % agarose gels, containing 0.8 μg/ml ethidium bromide, in order to

analyse amplicon size and primer specificity. The products were visualized using a long

wavelength UV light box (Bio-Rad Gel Doc EQ-system™, Bio-Rad Laboratories Inc., USA).

The fragments of interest were excised from the gel and purified using the FavorPrep Gel/PCR

Purification kit (FavorGenTM, Germany), according to the manufacturer’s instructions, if they

were to be cloned into pGEM®-T Easy for DNA sequencing (section 2.3.6), or the amplified

products were purified using the MSB® Spin PCRapace kit (STRATEC Molecular, Germany)

if they were to be sent directly for sequencing as PCR products.

4.3.5 CLONING AND RESTRICTION ENDONUCLEASE DIGESTIONS

For cloning, the fragments of interest were excised from the gel (section 4.3.4.2) and purified

using the FavorPrep Gel/PCR Purification kit (FavorGenTM, Germany) according to the

manufacturer’s instructions. The amplification products obtained from the primer sets

ADFWD/ADREV, CYCFWD/CYCREV, THIF/THIR, CINF/CINR, LACF/LACR and

ACYF/ACYR were ligated individually into the pGEM®-T plasmid as described in the


174

pGEM®-T Easy Vector System kit (Promega, USA). The ligation reaction was incubated at

22 °C for 14 h after which 10 ng of the reaction was transformed into E. coli α-Select Bronze

Efficiency Competent Cells (Bioline, UK) according to the manufacturer’s instructions.

The transformants were inoculated onto LB agar (Sambrook et al., 1989) supplemented with

100 µg/ml ampicillin, 40 µg/ml X-gal and 0.2 mM IPTG and incubated at 37 °C for 18 h.

Transformants harbouring recombinant pGEM®-T constructs were identified by blue/white

selection and white colonies were subcultured onto fresh LB agar plates supplemented with

100 µg/ml ampicillin, 40 µg/ml X-gal and 0.2 mM IPTG and incubated at 37 °C for 18 h to

confirm the white phenotype. The presence of the desired inserts was determined by

performing colony PCR using the M13F and M13R primer set (Table 2.1) in order to ensure

the correct size of the cloned fragment (Section 4.3.4.2).

Transformants identified as harbouring the correct recombinant constructs were inoculated into

5 ml LB broth containing 100 µg/ml ampicillin and cultured overnight with gentle shaking at

37 °C. Thereafter, plasmid DNA was isolated using the NucleoSpin Plasmid Isolation kit

(Machery Nagel, Germany) according to the manufacturer’s instructions and quantitated

spectrophotometrically as described before (section 2.3.2). One microgram of each of the

recombinant pGEM®-T vectors, individually carrying the THIF/THIR, LACF/LACR and

CINF/CINR amplification products, was subjected to a double restriction endonuclease

digestion with PstI and SacII (1.5 U of each enzyme) in the appropriate restriction buffer

overnight at 37 °C. The recombinant pGEM®-T vectors, individually carrying the

ADFWD/ADREV, CYCFWD/CYCREV and ACYF/ACYR amplification products, were

subjected to a single restriction endonuclease digestion with 1.5 U EcoRI in the appropriate

restriction buffer overnight at 37 °C. Each reaction was subjected to agarose gel

electrophoresis as described earlier and the desired inserts obtained from the restriction

endonuclease digestions were excised from the gel and purified using the Favorgen Gel/PCR

Purification Kit (FavorgenTM, Germany). The purified inserts were ligated into the plasmid

vector, pOJ260, which had been digested overnight at 37 oC with 1.5 U of EcoRI or a double

digestion consisting of SacII and PstI and thereafter dephosphorylated using rAPid Alkaline

Phosphatase (Roche, Switzerland) according to the manufacturer’s instructions. The alkaline

phosphatase incubation period was 24 h at 37 oC instead of the recommended 1 h.


175

Subsequently, ligation of each of the digested purified inserts into the dephosphorylated

pOJ260 vector was performed according to either the sticky-end or blunt-end protocol for the

Rapid DNA Ligation Kit (Thermo Fisher Scientific, USA) for 14 h at 4 oC, after which 10 ng

of the reaction was transformed into chemically competent E. coli α-Select Bronze Efficiency

Competent Cells (Bioline, UK) according to the manufacturer’s instructions. The

transformants were inoculated onto LB agar supplemented with 50 µg/ml apramycin, 40 µg/ml

X-gal and 0.2 mM IPTG and incubated at 37 °C for 18 h. Transformants harbouring

recombinant pOJ260 constructs were identified by blue/white selection and white colonies

were subcultured onto fresh LB plates supplemented with 50 µg/ml apramycin, 40 µg/ml X-

gal and 0.2 mM IPTG and incubated at 37 °C for 18 h to confirm the white phenotype.

Transformants with a white phenotype were identified as harbouring the correct recombinant

constructs and were inoculated into 5 ml LB broth containing 50 µg/ml apramycin and cultured

overnight with shaking at 37 °C. Thereafter, plasmid DNA was isolated using the NucleoSpin

Plasmid Isolation kit (Machery Nagel, Germany) according to the manufacturer’s instructions

and quantitated spectrophotometrically as described before (section 2.3.2). The recombinant

constructs carrying the amplification products obtained from the THIF/THIR, CINF/CINR,

LACF/LACR, ACYF/ACYR, CYCFWD/CYCREV and ADFWD/ADREV primer sets were

designated pOJTHI, pOJCIN, pOJLAC, pOJACY, pOJCYC and pOJA99, respectively (Table

4.1) and sequenced by the dideoxy chain-termination method (Sanger et al., 1977) on an

Applied Biosystems Big Dye terminator v3.1 DNA sequencer using BIOLINE Half Dye Mix

(Macrogen Inc., South Korea) using the appropriate gene specific primers in order to confirm

the presence of the desired inserts.

Additionally, the pGEMA-16, pGEMA-18, pGEMA-28, pGEMA-7 and pGEMAD-2 A

domain clones and the pGEM-PAAK clone described in Chapter 2 (section 2.3.8.2) were

subjected to restriction endonuclease digestion with 1.5 U EcoRI and the appropriate restriction

buffer at 37 °C overnight. The DNA samples were subjected to agarose gel electrophoresis,

excised from the gel and purified as described above. Each of the inserts was ligated into

dephosphorylated pOJ260, which had been subjected to restriction endonuclease digestion with

EcoRI, and transformed into chemically competent E. coli α-Select Bronze Efficiency

Competent Cells (Bioline, UK) according to the manufacturer’s instructions. Selection of

positive transformants carrying the desired insert and isolation of plasmid DNA was performed


176

as described above and the recombinant constructs carrying the A16, A18, A28, A7, AD2 and

paaK insert sequences were designated pOJA16, pOJA18, pOJA28, pOJA7, pOJAD2 and

pOJPAAK.

Furthermore, the amplification product obtained from the ACYORF_F/ACYORF_R primer

set was ligated directly into the pJN100 plasmid, which had been digested with 1.5 U of each

of ClaI and HindIII in the appropriate restriction buffer overnight at 37 °C. The ligation was

performed at 4 °C for 18 h and thereafter 10 ng of the ligation product was transformed into

chemically competent E. coli α-Select Bronze Efficiency Competent Cells (Bioline, UK)

according to the manufacturer’s instructions. The transformants were inoculated onto LB agar

supplemented with 50 µg/ml apramycin, 40 µg/ml X-gal and 0.2 mM IPTG and incubated at

37 °C for 18 h. Transformants harbouring recombinant pJN100 constructs were identified by

colony PCR using the ACYF/ACYR primer set (section 4.3.4.2).

4.3.6 DETERMINATION OF THE ANTIBIOTIC SUSCEPTIBILITY OF

S. POLYANTIBIOTICUS SPRT

The antibiotic susceptibility of S. polyantibioticus SPRT was determined by inoculation onto

YEME agar containing 0, 10, 15, 20, 25, 30, 35, 40, 45 and 50 µg/ml of apramycin, hygromycin

B or kanamycin and incubating for 72 h at 30 °C. Subsequently, growth of S. polyantibioticus

SPRT was assessed to determine the susceptibility to each antibiotic.

4.3.7 KNOCKOUT CONSTRUCTION BY GENE DISRUPTION EXPERIMENTS

4.3.7.1 CONJUGATION

4.3.7.1.1 TRANSFORMATION OF PLASMID DNA INTO E. COLI

ET12567/pUZ8002

Chemically competent E. coli ET12567/pUZ8002 cells were prepared according to the method

described by Dagert and Ehrlich (1979). The plasmids designated pOJA16, pOJA18, pOJA28,

pOJA7, pOJAD2, pOJPAAK, pOJTHI, pOJCIN, pOJLAC, pOJACY, pOJCYC, pOJA99 and


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pJNACY were transformed into chemically competent E. coli ET12567/pUZ8002 cells for

subsequent intergeneric conjugation.

4.3.7.1.2 CONJUGATION BETWEEN E. COLI ET12567/pUZ8002

AND E. COLI JM109

In order to test the conjugal ability of E. coli ET12567/pUZ8002, conjugation between E. coli

ET12567/pUZ8002 and E. coli JM109 was performed according to the method described by

Zhang et al. (2013) with some modifications. Briefly, the donor strain, E. coli

ET12567/pUZ8002 harbouring the plasmid pOJAD2, was cultured in LB broth containing 50

µg/ml apramycin, 100 µg/ml chloramphenicol and 25 µg/ml kanamycin, while the recipient

strain, E. coli JM109, was cultured in LB broth without antibiotics at 37 °C with shaking at

200 rpm until an OD600nm = 0.5 was reached (mid-exponential phase). The cells were collected

by centrifugation at 5000 rpm for 5 min, washed once with an equal volume of LB broth

(without antibiotics) and resuspended in 1 ml LB medium before 50 µl of the donor strain was

mixed with 50 µl of the recipient in a 1.5 ml microcentrifuge tube and supplemented with 900

µl LB broth which had been pre-warmed to 37 °C. After mixing, the cells were incubated at

37 °C without shaking for 24 h. The conjugation process was interrupted by vortexing for 10

sec and the mixture was immediately serially diluted 10-fold and plated on LB agar containing

50 µg/ml nalidixic acid and 50 µg/ml apramycin in order to select for the recipient strain (strain

JM109 has a DNA gyrase mutation which makes it resistant to nalidixic acid).

4.3.7.1.3 INTERGENERIC CONJUGATION BETWEEN E. COLI

AND S. POLYANTIBIOTICUS SPRT

Classical intergeneric conjugation was performed between E. coli ET12567/pUZ8002 and

S. polyantibioticus SPRT and between E. coli ET12567/pUZ8002 and S. coelicolor A3(2),

according to the method described by Flett et al. (1997). Conjugation was also performed

between E. coli S17-1 and both Streptomyces strains according to the method described by

Mazodier et al. (1989). Briefly for both methods, the donor E. coli strain (ET12567/pUZ8002

or S17-1 carrying pJN100) was cultured in 25 ml LB broth supplemented with 50 µg/ml

apramycin, 34 µg/ml chloramphenicol and 50 µg/ml kanamycin to an OD600nm = 0.5, pelleted

by centrifugation at 5000 rpm for 5 min, washed twice with LB broth and resuspended in 1 ml


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LB. Aliquots of S. polyantibioticus SPRT and S. coelicolor A3(2) spore suspensions, which

had been stored at -20 °C, were used as recipients. Spores were induced to germinate by heat-

shock at 50 °C for 10, 20, 30 or 60 min, after which the donor E. coli cells were added to the

prepared spores and the mixture was inoculated onto MS + 20 mM MgCl2 plates. The

conjugation plates were incubated for 16 h at 30 °C, after which the surface of each plate was

overlaid with 1 ml of sterile dH20 containing 500 µg nalidixic acid and 1 mg apramycin. The

plates were incubated for a further 96 h at 30 °C and the exconjugant colonies were counted.

The classical conjugation method was modified in order to obtain S. polyantibioticus SPRT

exconjugants by growing the donor E. coli culture to an OD600nm of 0.3, 0.4 or 0.6 (instead of

0.5, by decreasing the centrifugation speed to 3500 rpm (instead of 5000 rpm), by using a

culture of S. polyantibioticus SPRT which had been grown for 5 h, 12 h, 18 h, 24 h, 48 h and

72 h (instead of using a spore preparation), by cultivating S. polyantibioticus SPRT mycelia in

YEME, V or SMC media, and by plating the conjugation mixture on 7H9, YEME or ISP4

supplemented with 10 mM or 20 mM MgCl2 (instead of MS supplemented with 10 mM or 20

mM MgCl2). All of these modifications were tested as individual changes to the original

method and in different combinations in order to optimise the method for transformation of S.

polyantibioticus SPRT.

A reproducible method for intergeneric conjugation between E. coli ET12567/pUZ8002 and S.

polyantibioticus SPRT was finally established based on the methods described by Marcone et

al. (2010) and Du et al. (2012). Briefly, a culture of the donor strain, E. coli ET12567/pUZ8002

containing the selected plasmid was cultivated in 25 ml LB broth supplemented with 50 µg/ml

apramycin, 34 µg/ml chloramphenicol and 50 µg/ml kanamycin to an OD600nm = 0.4

(approximately 1 x 107 cells/ml). Cells were collected by centrifugation at 3500 rpm for 7 min,

washed twice with an equal volume of LB broth and resuspended in 1 ml LB broth. S.

polyantibioticus SPRT mycelia were prepared as follows: fresh spores were scraped off the

surface of an ISP4 plate and used to inoculate 25 ml SMC medium, containing 10.3 % sucrose

and incubated at 30 °C on a rotary shaker at 200 rpm for 18 h (exponential phase). Mycelia

were collected by centrifugation at 10 000 rpm for 10 min at 4 °C and resuspended in 2 ml ice

cold LB. For conjugation, 0.5 ml donor E. coli ET12567/pUZ8002 cells carrying the selected

plasmid (OD600nm = 0.4) were added to 0.5 ml S. polyantibioticus mycelium and incubated in a

2 ml microcentrifuge tube at 30 °C for 1 h before serially diluting 1000 fold in LB broth and


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plating on YEME agar supplemented with 10 mM or 20 mM MgCl2. The conjugation plates

were incubated at 30 °C for 18 h and then overlaid with 25 µg/ml nalidixic acid and 25 µg/ml

apramycin. The plates were incubated for a further 72-96 h at 30 °C before single Streptomyces

colonies were sub-inoculated onto fresh YEME plates containing 50 µg/ml nalidixic acid and

30 µg/ml apramycin to confirm the single crossover exconjugants. The conjugation frequency

was calculated as the number of exconjugants per total number of donor E. coli cells.

To confirm the chromosomal integration of the pOJ260 and pJN100 derivative plasmids,

gDNA was extracted from the exconjugants using the method described in section 2.3.2 and

PCR amplification using the pOJFWD/pOJREV primers was performed (section 4.3.7.1.4).

4.3.7.1.4 CONFIRMATION OF SINGLE CROSSOVER EXCONJUGANTS

BY PCR AMPLIFICATION

Amplification of gDNA isolated from S. polyantibioticus mutant strains ∆AD2, ∆A16, ∆A18,

∆A28, ∆A7, ∆PAAK, ∆THI, ∆CIN, ∆LAC, ∆ACY, ∆CYC and ∆A99 was performed using the

POJFWD primer in combination with the respective reverse gene specific primer of interest:

A7R for AD2, A16, A18, A28 and A7, PAAKREV for PAAK, THIR for THI, CINR for CIN,

LACR for LAC, ACYR for ACY, CYCREV for CYC and ADREV for A99, in order to confirm

the integration of the target gene within the mutant S. polyantibioticus genomes. Additionally,

the POJREV primer was used in combination with the respective forward gene specific primer

of interest: A3F for AD2, A16, A18, A28 and A7, PAAKFWD for PAAK, THIF for THI, CINF

for CIN, LACF for LAC, ACYF for ACY, CYCFWD for CYC and ADFWD for A99, in an

amplification reaction to confirm the integration of the target within the mutant S.

polyantibioticus genomes.

The cycling conditions used for the amplification reactions were performed as follows: initial


annealing at 56 oC for 30 s and elongation at 72 oC for 60 s, with a final elongation at 72 oC for

5 min. PCR reactions consisted of: 200 ng of DNA, 2 U SuperThem Taq polymerase (JMR

Holdings, USA), 1.5 μM of each primer, 0.2 mM of each dNTP and 3 mM MgCl2 in a total

volume of 50 μl.


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All PCR amplification products were resolved by electrophoresis alongside a λ-PstI molecular

marker on 0.8 % agarose gels containing 0.8 μg/ml ethidium bromide in order to analyse

amplicon size. The products were visualized using a long wavelength UV light box (Bio-Rad

Gel Doc EQ-system™, Bio-Rad Laboratories Inc, USA) and excised from the agarose gel,

purified using the Favorgen Gel/PCR Purification Kit (FavorgenTM, Germany) and sequenced

by the dideoxy chain-termination method (Sanger et al., 1977) on an Applied Biosystems Big

Dye terminator v3.1 DNA sequencer using BIOLINE Half Dye Mix (Macrogen Inc., South

Korea).

4.3.7.2 ELECTROPORATION

4.3.7.2.1 PREPARATION OF PLASMID DNA FOR

ELECTROPORATION

The plasmids, pJN100 and pJNHYG, were transformed into E. coli dam-/dcm- chemically

competent cells, according to the method described by Dagert and Ehrlich, (1979), in order to

generate unmethylated plasmid DNA, which was deemed necessary for efficient

electroporation (Spath et al., 2012). Thereafter, plasmid DNA was isolated using the

NucleoSpin Plasmid Isolation kit (Machery Nagel, Germany) according to the manufacturer’s

instructions and quantitated spectrophotometrically as described before (section 2.3.2).

4.3.7.2.2 ELECTROPORATION

Electroporation of plasmid DNA into S. polyantibioticus SPRT and S. coelicolor A3(2) was

initially performed based on the method described by Pigac & Schrempf (1995). Briefly, S.

polyantibioticus SPRT and S. coelicolor A3(2) mycelia was individually cultured in 25 ml CRM

at 30 °C on a rotary shaker at 220 rpm for 24-72 h. Each culture was harvested by

centrifugation at 10 000 rpm at 4 °C, washed once with 25 ml ice cold 10 % sucrose, centrifuged

at 10 000 rpm at 4 °C, re-suspended in 12.5 ml 15 % glycerol, centrifuged at 10 000 rpm at 4

°C and finally re-suspended in 2 ml ice cold 15 % glycerol containing 100 µg/ml lysozyme.

The mycelial suspension was incubated at 37 °C for 1 h and then washed twice with ice-cold

15 % glycerol by centrifugation at 10 000 rpm at 4 °C, before re-suspension in 1 ml of the

electroporation buffer, which consisted of sterile de-ionized dH20 containing 30 % PEG-1000,


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10 % glycerol and 6.5 % sucrose. The mycelial suspension was dispensed into 50 µl aliquots

in 1.5 ml microcentrifuge tubes and immediately stored at -80 °C overnight. Subsequently, a

50 µl aliquot was thawed on ice and 10 ng to 1 µg of plasmid DNA (pJN100 or pJNHYG) was

added to it, before the mixture was transferred into a 2 mm-gapped electrocuvette (Bio-Rad

Laboratories Inc., USA) and subjected to an electrical pulse ranging from 0 to 12.5 kV/cm

using a Gene Pulser (Bio-Rad Laboratories Inc., USA), which was connected to a pulse

controller (25 µF capacitor) with a parallel resistor setting of 200, 400, 600 or 800 Ω. The

pulsed mycelium was immediately diluted with ice cold 0.75 ml CRM and incubated on a

rotary shaker at 220 rpm for 3 h at 30 °C. Before plating, CRM was added to a final volume

of 1 ml and dilutions were inoculated onto TSB plates containing 30 µg/ml apramycin. Control

reactions were performed by omitting either the plasmid DNA or the electrical pulse.

An alternative method described by Tyurin et al. (1995) for electroporation of freshly

germinated mycelial fragments was also performed. Briefly, freshly harvested

S. polyantibioticus SPRT and S. coelicolor A3(2) spores were inoculated individually into 25

ml TSB and incubated on a rotary shaker (220 rpm) at 30 °C for 3-48 h. The cells were

harvested by centrifugation at 10 000 rpm (4 °C) for 10 min, followed by washing twice with

0.15 M sucrose (centrifugation at 10 000 rpm for 10 min each time) and resuspension of the

pellet in the electroporation buffer consisting of sterile de-ionized dH20 containing 7 mM

HEPES, 75 mM sucrose and 1 mM MgCl2. The mycelial suspension was dispensed into 50 µl

aliquots and stored at -80°C overnight. Subsequently, 10 ng to 1 µg of plasmid DNA was

added to a thawed 50 µl mycelial aliquot and pulsed as described above. The pulsed mycelia

were immediately diluted with 0.5 ml TSB, left on ice for 10 min and incubated at 30 °C for

1.5 h. Each electroporation reaction was inoculated onto TSB plates containing 30 µg/ml

apramycin. Controls were performed by omitting either the plasmid DNA or the electrical

pulse.

Another two methods described by Mazy-Servais et al. (1997) and Ma et al. (2013) were also

tested. For the method described by Mazy-Servais et al. (1997), freshly harvested S.

polyantibioticus SPRT spores were inoculated into 25 ml YEME medium supplemented with

34 % sucrose and 0.5 % glycine and incubated on a rotary shaker (220 rpm) at 30 °C for 12-72

h. The mycelia were harvested by centrifugation at 10 000 rpm (4 °C) for 15 min, followed by

washing three times with an equal volume of sterile dH20 (centrifugation at 10 000 rpm for 10


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min each time). Two different treatments were then applied to the cells: lysozyme digestion

or suspension in PEG-supplemented electroporation buffer. In the case of the lysozyme

treatment, cells were resuspended in 25 ml electroporation buffer (10 % sucrose, 15 % glycerol

and 3 mM NaH2PO4-Na2HPO4 buffer, pH 7.4) containing 0.5 mg/ml lysozyme and incubated

at 37 °C for 1 h, before the cells were harvested by centrifugation at 10 000 rpm (4 °C) for 15

min. The cells were resuspended in 1 ml ice cold electroporation buffer and distributed into

50 µl aliquots before electroporation. In the case of PEG treatment, cells were resuspended in

25 ml ice cold electroporation buffer, subjected to the same centrifugation conditions

mentioned above and resuspended in 1 ml electroporation buffer containing 28.5 % PEG-1000,

before distribution into 50 µl aliquots. Ten nanograms (10 ng) to one microgram (1 µg) of

plasmid DNA was then added to both sets of treated aliquots, which were kept on ice for 1 min

before the mixture was transferred to an electrocuvette and a single electrical pulse was applied

according to the conditions shown in Table 4.3. The pulsed mycelia were diluted with ice cold

0.4 ml SOC solution, kept on ice for 5 min and plated onto R2YE agar plates containing 30

µg/ml apramycin.

Table 4.3 Electroporation conditions used in this study Parallel resistance (Ω) Pulse (kV/cm) Capacitance (µF)

200 7.5 25

200 10 25

200 12.5 25

400 5 25

400 7.5 25

400 10 25

400 12.5 25

600 5 25

600 7.5 25

600 10 25

600 12.5 25

800 2.5 25

800 5 25

800 7.5 25

800 10 25

800 12.5 25


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The method described by Ma et al. (2013) was performed in a similar manner to the method

described by Tyurin et al. (1995) with some modifications. Briefly, the resuspension step

consisted of resuspending the cell pellet in 15 % glycerol containing 25 mg/ml lysozyme and

10 µg/ml penicillin G, incubating at 37 °C overnight and then for a further 2 h at room

temperature. Furthermore, the electroporation buffer consisted of 10 % PEG-1000, 10 %

glycerol and 6.5 % sucrose, each electroporated sample was diluted in 1 ml CP medium (1 %

glucose, 0.2 % tryptone, 0.4 % yeast extract, 0.05 % MgSO4.7H2O, 0.05 % K2HPO4, 0.05 %

NaCl per litre of dH2O, pH 7.2) instead of CRM and was plated on R2YE and YEME solid

media. In addition, modifications to the above mentioned methods were performed by replacing the

wash buffers with 1 M sorbitol supplemented with 2, 4, 6 or 8 % DMSO, as well as with 1 mM

citrate supplemented with 16 % raftilose and replacing the initial culture medium with TSB

supplemented with 0.24 mM threonine and 1 % glycine. Other modifications to the

electroporation conditions included double pulsing each sample and the addition of 5 µg of

TypeOne Restriction Inhibitor (Epicentre, USA) to each electroporation reaction before

pulsing in order to circumvent potential R-M systems.

4.3.7.3 PROTOPLAST TRANSFORMATION

4.3.7.3.1 PREPARATION OF PROTOPLASTS

S. polyantibioticus SPRT and S. coelicolor A3(2) protoplasts were prepared according to the

method described by Marcone et al. (2010) with some modifications. Briefly, a glycerol spore

preparation (Kieser et al., 2000) of each strain was inoculated into 25 ml V medium and

cultured for 36-48 h at 30 °C on a rotary shaker (220 rpm). The culture was centrifuged at

4500 rpm for 10 min at 4 °C and washed once (centrifugation at 3250 rpm for 10 min) with 25

ml P medium (103 g sucrose, 0.25 g K2SO4, 2.02 g MgCl2.6H2O, 2 ml trace element solution,

1 ml 0.5 % KH2PO4, 3.68 % CaCl2.2H2O, 10 ml 5.73 % TES buffer per litre of dH2O, pH 7.2)

(Okanishi et al., 1974). In order to achieve cell-wall digestion, 12.5 ml P medium (consisting

of 20 mg/ml lysozyme, 0.018 mg/ml mutanolysin and 100 mg/l pluronic) was added to the cell

pellet and incubated at 30 °C on a rotary shaker (50 rpm) for 48 h. Protoplast formation was

monitored by using an Olympus CH20 microscope at 1000 x magnification. Protoplasts were


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detached from residual mycelium clumps by gently drawing through a 5 ml glass pipette tip

and then filtering through sterile cotton wool. Protoplasts were harvested by centrifugation at

4500 rpm for 10 min at 4 °C and finally resuspended in 1 ml P medium. Fifty microlitre (50

µl) aliquots of the protoplast suspension were added to microcentrifuge tubes, which were

placed in a beaker of ice and then stored at -80 °C until needed.

4.3.7.3.2 PROTOPLAST TRANSFORMATION

One microgram of plasmid DNA (approximately 5 µl) was added to each protoplast suspension

(section 4.3.7.3.1) in a microcentrifuge tube, followed by the addition of 200 µl T buffer and

gentle mixing by pipetting up and down. After incubation at room temperature for 2 min, the

transformation mixture was inoculated onto R2YE medium (Kieser et al., 2000) or VMSO.1

agar medium (Marcone et al., 2010). The plates were incubated at 30 °C for 20 h and then

overlaid with 30 µg/ml apramycin.

4.3.8 FERMENTATION AND ISOLATION OF DPO

Spores and mycelial mass were collected from S. polyantibioticus strains SPRT, ∆AD2, ∆A16,

∆A18, ∆A28, ∆A7, ∆PAAK, ∆CIN, ∆LAC, ∆CYC, ∆A99, ∆ACY, ∆THI and PJNACY from

10 day old ISP4 agar plates and heavy suspensions were made in 2 ml microcentrifuge tubes

containing 1.5 ml sterile distilled water. The spore suspension of each strain was used to

inoculate a seed culture of 25 ml Hacène’s medium (HM; 5 g glucose, 4 g yeast extract powder,

10 g malt extract powder and 1 g NaCl per litre of dH2O, pH 7.0) (Hacène & Lefebvre, 1995)

in a 250 ml Erlenmeyer flask. The flask was incubated at 30 °C for 48 h on a rotary shaker,

before inoculation into a 5 L Erlenmeyer flask containing 1 litre of HM. The flask was

incubated at 30 °C on a rotary shaker for an additional 192 h (8 days) for a total fermentation

time of 10 days.

The purity of each culture was confirmed by performing a standard Gram stain, after which

DPO was isolated and purified from the cultures according to the method depicted in Figure

4.5 (method adapted from le Roes, 2005). Briefly, the culture was filtered through a 1 x 4 sized

coffee filter (House of Coffees, RSA), after which DPO was extracted from the mycelial mass

with methanol and from the culture filtrate with ethyl acetate by stirring at room temperature


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on a magnetic stirrer overnight. After concentration to 25 ml, by evaporation in a fumehood,

the methanol and ethyl acetate extracts were combined, the pH was adjusted to 7.0 (monitored

with pH strips, Merck, Germany) and the mixture was re-extracted with 500 ml toluene by

stirring at room temperature on a magnetic stirrer overnight. The toluene extract was

concentrated to 50 ml by evaporation in a fumehood and extracted with 0.1 M sodium acetate

buffer (pH 3.5) by stirring at room temperature on a magnetic stirrer overnight. The toluene

layer was concentrated to 5 ml by evaporation in a fumehood and used directly in subsequent

HPLC and TLC bioautography analysis experiments.

In addition, following the isolation of pure DPO from strains S. polyantibioticus SPRT,

S. polyantibioticus ∆AD2, S. polyantibioticus ∆A18, S. polyantibioticus ∆A16,

S. polyantibioticus ∆A28, S. polyantibioticus ∆A7, S. polyantibioticus ∆PAAK,

S. polyantibioticus ∆CYC, S. polyantibioticus ∆A99, S. polyantibioticus ∆ACY,

S. polyantibioticus ∆LAC, S. polyantibioticus ∆CIN and S. polyantibioticus ∆THI, each DPO

sample was subjected to UV spectrophotometry at a wavelength of 280 nm using the

Nanodrop® ND-1000 Spectrophotometer (Coleman Technologies Inc., USA).


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Figure 4.5 Schematic diagram depicting the isolation and purification of DPO.

4.3.9 HIGH PERFORMANCE LIQUID CHROMATOGRAPHY (HPLC)

Analytical reverse phase-HPLC analysis of a pure DPO sample (approximately 1 µg/ml)

isolated from S. polyantibioticus SPRT (section 4.3.8) and a commercial sample of DPO

(Sigma-Aldrich, USA, catalogue number: D210404) (1 mg/ml dissolved in toluene) was

carried out on an Agilent system (Agilent Technologies, USA) using a Vydac-C18 column (5

µm particle size, 4.66 x 250 mm) with 50 % acetonitrile as the mobile phase. The flow rate was

1 ml/min and DPO detection was at 280 nm.

http://www.sigmaaldrich.com/catalog/product/aldrich/d210404?lang=&region=&cm_sp=abstract-_-3684951-_-D210404


187

4.3.10 THIN LAYER CHROMATOGRAPHY (TLC) BIOAUTOGRAPHY ANALYSIS

Each pure DPO sample (approximately 1 mg/ml) (section 4.3.8), a commercial DPO sample

(Sigma-Aldrich, USA) (1 mg/ml dissolved in toluene) and the solvent, toluene, to serve as a

negative control, was applied to the surface of a silica gel 60 F254 TLC plate (Merck, Germany,

catalogue number: 1055530001) and allowed to dry in a fumehood for 15 min at room

temperature. The plates were developed in a pre-saturated solvent chamber using ethyl acetate

as the mobile phase until the solvent front reached approximately 1 cm from the top of the

plates. The developed TLC plates were removed from the chamber and allowed to air-dry for

30 min, before being subjected to bioautography analysis against M. aurum A+.

M. aurum A+ was inoculated in LB broth and incubated at 37 °C with shaking for two days.

After performing a standard Gram stain to confirm the purity of the culture, the optical density

of the culture was determined on a Novaspec II spectrophotometer (Pharmacia Biotech,

Sweden) at a wavelength of 600 nm. The culture was diluted to OD600nm = 0.5 using sterile LB

broth. The test bacterium was applied to the surface of the TLC plate (containing the DPO test

sample, commercial DPO sample and toluene) with sterile non-absorbent cotton wool, the TLC

plate was placed in a plastic sealable container lined with moist paper towel and incubated

overnight at 37 °C (about 18 h).

Thiazolyl blue (MTT; Sigma-Aldrich, USA, catalogue number: M2128), dissolved in

phosphate buffered saline (4.26 g Na2HPO4.7H2O, 2.27 g KH2PO4, 8 g NaCl per litre of dH2O,

pH 7.0) at a final concentration of 0.25 % w/v, was applied to the plates using sterile non-

absorbent cotton wool and the plates were incubated at 37 °C for a further 2 h. Colour changes

were noted: MTT is yellow and turns purple when reduced, thereby indicating the presence of

living cells, whereas white areas on the plate indicate zones where the test bacteria have been

killed.


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4.4.1 DETERMINATION OF THE ANTIBIOTIC SUSCEPTIBILITY OF

S. POLYANTIBIOTICUS SPRT

The antibiotic susceptibility of S. polyantibioticus SPRT was determined against apramycin,

hygromycin B and kanamycin in order to establish an appropriate marker to select against

untransformed cells in each transformation experiment (Table 4.4).

Table 4.4 The antibiotic susceptibility of S. polyantibioticus SPRT against various

antibiotics Antibiotic Concentration (µg/ml) Growth

Apramycin 20 -

Kanamycin 50 -

Hygromycin B 100 -

S. polyantibioticus SPRT exhibited sensitivity to apramycin, kanamycin and hygromycin B at

concentrations of 20 µg/ml, 50 µg/ml and 100 µg/ml, respectively. Apramycin was chosen as

the selectable marker for all subsequent gene disruption experiments due to the extensive

availability of E. coli-Streptomyces shuttle vectors carrying the gene for apramycin resistance.

4.4.2 THE DEVELOPMENT OF AN OPTIMISED TRANSFORMATION

PROTOCOL FOR S. POLYANTIBIOTICUS SPRT

4.4.2.1 ELECTROPRATION AND PROTOPLAST TRANSFORMATION

In order to identify the genes involved in DPO biosynthesis, an efficient DNA transformation

protocol was required for the introduction of foreign DNA into S. polyantibioticus SPRT, to be

able to disrupt genes to prove their involvement in the DPO biosynthetic pathway. Although

published transformation protocols exist for the introduction of DNA into streptomycetes, there


189

is no method that is generally applicable to all species. Due to the fact that S. polyantibioticus

SPRT is a novel antibiotic-producing actinomycete, the establishment of a transformation

protocol was required to make this strain amenable to genetic modifications.

Various methods for the delivery of pJN100 DNA were applied to S. polyantibioticus SPRT

cells in this study. Electroporation was the first method to be employed for transformation of

DNA into S. polyantibioticus SPRT, as it has been used in numerous Streptomyces species,

including S. coelicolor A3(2), which was used as a positive control in the present study. The

optimization of the classical electroporation methods described by Pigac & Schrempf (1995)

and Tyurin et al. (1995) proved successful for transforming plasmid DNA into S. coelicolor

A3(2). The highest number of S. coelicolor A3(2) transformants per µg of plasmid DNA was

obtained using a field strength of 7.5 kV/cm, a parallel resistor setting of 800 Ω and a time

constant of 18 ms (Figure 4.6). These optimized conditions were applied to the electroporation

of S. polyantibioticus SPRT cells without success.

Subsequently, an extensive optimization of four electroporation protocols was conducted.

Addition of various agents that affect cell wall structure to the growth medium has been shown

to enhance the electrotransformation of Gram-positive bacteria. High concentrations of glycine

(1-4 % w/v) have been used to successfully inhibit cell wall synthesis and it has been reported

that the addition of glycine and the osmotic stabilizer, sucrose, resulted in an increased

transformation efficiency of Lactococcus lactis (Papagianni et al., 2007; Holo and Nes, 1989).

Furthermore, supplementation of the growth medium with glycine and L-threonine produced

B. subtilis cells that could be electrotransformed much more efficiently at frequencies up to 2.5

x 103 transformants/µg of plasmid DNA (McDonald et al., 1995). Additionally, the

supplementation of growth media with penicillin G, which affects the cross-linking of the cell

wall in Gram-positive bacteria, was shown to enhance the transformation frequency in

Rhodococcus rhodochrous CF222 (Sunairi et al., 1996).

Initially, the filamentous growth of S. polyantibioticus SPRT proved an obstacle for all of the

methods, as the filaments aggregated. However, the addition of PEG-1000, sucrose and/or

glycine was sufficient to impair the formation of the filaments. It was therefore noted that the

most appropriate time span for electroporation was within the first 24 h of growth due to the


190

fact that a longer incubation time resulted in a high cell density culture containing aggregates

of intertwined hyphae, which caused arcing during electroporation.

In order to circumvent the potent restriction-modification systems present in many

Streptomyces species, all plasmid DNA used for electroporation into S. polyantibioticus SPRT

was isolated from E. coli dam- dcm- cells. Additionally, a restriction inhibitor, TypeOne

Restriction Inhibitor (Epicentre, USA), was incorporated into each electroporation reaction in

order to block the DNA binding site of type 1 R-M systems and inhibit cleavage of unmodified

DNA.

However, despite efforts to optimize an efficient electroporation protocol for

S. polyantibioticus SPRT, none proved successful. Consequently, in an effort to avoid the

problems caused by cell filaments and/or cell wall structures, protoplasts were used for the

introduction of plasmid DNA into S. polyantibioticus SPRT. Protoplast formation was achieved

after a period of 48 h in S. polyantibioticus SPRT, which was microscopically observed every

12 h up until the minimum required time for protoplast formation of 48 h, in contrast to the

rapid protoplast formation, approximately 25 min, observed in S. coelicolor A3(2). Despite

the success in preparing S. polyantibioticus SPRT protoplasts using standard procedures, they

could not be regenerated on the standard regeneration medium, R2YE (Kieser et al., 2000) or

the alternative medium, VMSO.1 (Marcone et al., 2010) under conditions where protoplasts of

other Streptomyces spp. were regenerated. Thus, it was never possible to test protoplast

transformation of S. polyantibioticus SPRT cells.


191

Figure 4.6 Effects of various electroporation parameters on the transformation efficiency of S. coelicolor

A3(2). (A) Effect of the initial voltage of the applied electrical pulse on transformation

efficiency of the electroporated cells at 25 µF and 800 Ω. (B) Effect of the external parallel

resistance on transformation efficiency of the electroporated cells at 25 µF and 7.5 kV/cm. (C)

Effect of the electrical pulse duration (time constant) on transformation efficiency of

electroporated cells at 25 µF and 7.5 kV/cm.

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14

Tran

sfo

rman

ts/µ

g D

NA

Field strength (kV/cm)

A

0

20

40

60

80

100

120

140

0 200 400 600 800 1000

Tran

sfo

rman

ts/µ

g D

NA

Parallel resistor setting

B

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14 16 18 20

Tran

sfo

rman

ts/µ

g D

NA

Time constant (ms)

C


192

It is possible that the inability to transform DNA into S. polyantibioticus SPRT, using

electroporation, could be attributed to the inefficient expression of the heterologous apramycin-

resistance gene promoter in plasmid pJN100 when transformed into S. polyantibioticus SPRT.

The apramycin resistance gene was originally isolated from Klebsiella pneumoniae and it has

previously been reported that when the promoter being used is heterologous to the host strain,

expression may be feeble or non-existent due to unknown reasons (Wilkinson et al., 2002).

The apramycin resistance gene cassette in pJN100 was therefore replaced with the hygromycin

resistance cassette (originally isolated from Streptomyces hygroscopicus) to generate the

modified vector, pJNHYG. It was hoped that the hygromycin resistance gene would be more

efficiently expressed in S. polyantibioticus SPRT, due to the fact that it was derived from the

same genus, thereby allowing transformation and integration of pJNHYG in S. polyantibioticus

SPRT. However, no exconjugants were observed after transformation with pJNHYG,

suggesting that the problem was one of getting plasmid DNA into S. polyantibioticus SPRT

rather than one of antibiotic selection.

4.4.2.2 INTERGENERIC CONJUGATION

Intergeneric conjugation has been used to circumvent plasmid DNA transformation problems

in Streptomyces strains that are recalcitrant to protoplast transformation, most likely due to the

fact that ssDNA is transferred thereby bypassing any R-M systems (Voeikova, 1999).

Additionally, intergeneric conjugation allows for the utilization of E. coli shuttle vectors

containing the oriT function that can be used for targeted gene disruption (Kieser et al., 2000).

Two E. coli strains were used as donors in intergeneric conjugations, S17-1 and

ET12567/pUZ8002, with S. coelicolor A3(2) and S. polyantibioticus SPRT as the recipient

strains. Additionally, the conjugal ability of E. coli ET12567/pUZ8002 harbouring pOJAD2

was determined by successful mating with E. coli JM109.

Donor cultures carrying pJN100 were mated individually with S. coelicolor A3(2) and

S. polyantibioticus SPRT. The E. coli S17-1 and ET12567/pUZ8002 strains were efficient in

transferring the pJN100 plasmid to S. coelicolor A3(2) using classical conjugation methods

with conjugation frequencies of 2.1 x 10-5 and 1.83 x 10-5 exconjugants per 1 x 107 donor E.

coli cells, respectively, which is comparable to the 1 x 10-5 exconjugants obtained by Flett et


193

al. (1997) (Figure 4.7). However, the transfer of pJN100 into S. polyantibioticus SPRT was

only successful using E. coli ET12567/pUZ8002 as the donor strain with a conjugation

frequency of 8.3 x 10-6 exconjugants per 1 x 107 donor E. coli cells (Figure 4.7). The

unsuccessful mating between E. coli S17-1 and S. polyantibioticus SPRT may have been due

to the fact that the vigorous growth of E. coli S17-1 caused the donor strain to rapidly reach

stationary phase and thereby overgrow relative to S. polyantibioticus SPRT, before E. coli-

streptomycete mating junctions had been established (Flett et al., 1997).

In contrast to the classical conjugation methods described by Mazodier et al. (1989) and Flett

et al. (1997), whereby a glycerol spore preparation of the recipient strain was subjected to heat

treatment to induce germination and thereafter mated directly with the donor E. coli strain,

freshly germinated S. polyantibioticus SPRT spores were inoculated into liquid growth medium

for cultivation for 18 h before mating took place. Furthermore, only liquid SMC medium

containing 10.3 % sucrose produced a dispersed culture of S. polyantibioticus SPRT mycelia

that promoted the transfer of plasmid DNA across the cell wall. No exconjugants were

observed when the S. polyantibioticus SPRT cells were grown in any other medium.

In addition, it has been reported that the mycelial age of the recipient strain is a critically

important factor for the uptake of plasmid DNA in terms of competence of the recipient cells.

Luo et al. (2009) reported that Nonomuraea mycelia collected during the exponential phase

were optimal for intergeneric conjugation, whereas mycelia collected from Streptomyces

peucetius after 34 h growth were most favourable for intergeneric conjugation (Paranthaman

et al., 2003). Indeed, it was observed that S. polyantibioticus SPRT mycelia collected after 18 h

were optimal for intergeneric conjugation with E. coli ET12567/pUZ8002/pJN100 with a

conjugation frequency of 8.3 x 10-6 exconjugants per 1 x 107 donor E. coli cells (Figure 4.8).

The conjugation frequency decreased 3.3-fold to 2.5 x 10-6 after 24 h of cultivation. Mycelia

collected earlier than 18 h or later than 24 h were not suitable for conjugation as no

exconjugants were observed.

Lastly, it has been observed that the solid medium on which the intergeneric conjugation takes

place has a significant influence on the conjugation frequency in various streptomycetes (Du

et al., 2012; Guan & Pettis, 2009; Kim et al., 2008; Choi et al., 2004; Kitani et al., 2000; Flett

et al., 1997). In this study, four solid media, MS, YEME, 7H9 and ISP Medium 4, each

supplemented with either 10 mM MgCl2 or 20 mM MgCl2, were tested in order to determine


194

which one promoted intergeneric conjugation between E. coli ET12567/pUZ8002/pJN100 and

S. polyantibioticus SPRT the most. Exconjugants were only obtained on YEME and 7H9

media, while no exconjugants were observed on MS or ISP4 media (Figure 4.9). YEME media

supplemented with 20 mM MgCl2 proved to be optimal for the conjugation of E. coli

ET12567/pUZ8002/pJN100 and S. polyantibioticus SPRT with a conjugation frequency of 8.2

x 10-6 exconjugants per 1 x 107 donor E. coli cells, 1.1-fold higher than that of YEME

supplemented with 10 mM MgCl2 and 2.3-fold higher than 7H9 medium supplemented with

10 mM MgCl2 (conjugation frequency of 3.5 x 10-6 exconjugants per 1 x 107 donor E. coli

cells). No significant differences were observed between media supplemented with 10 mM

MgCl2 or 20 mM MgCl2.

Figure 4.7 Effect of E. coli donor on intergeneric conjugation with S. coelicolor A3(2) and

S. polyantibioticus SPRT. The data are presented as the mean ± SEM of three independent

experiments of the number of S. polyantibioticus SPRT exconjugants observed per 1 x 107 donor

E. coli cells. SC denotes S.coelicolor A3(2), SPR denotes S. polyantibioticus SPRT, S17 denotes

E. coli S17-1/pJN100 and ET denotes E. coli ET12567/pUZ8002/pJN100.

0.0E+00

5.0E-06

1.0E-05

1.5E-05

2.0E-05

2.5E-05

SC + S17 SC + ET SPR + S17 SPR + ET

Co

nju

gati

on

fre

qu

ency


195

Figure 4.8 Effect of the mycelial age of the recipient strain, S. polyantibioticus SPRT, on intergeneric

conjugation with E. coli ET12567/pUZ8002/pJN100. The data are presented as the mean ± SEM of three independent experiments of the number of S. polyantibioticus SPRT exconjugants

observed per 1 x 107 donor E. coli cells.

0.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

6.0E-06

7.0E-06

8.0E-06

9.0E-06

5 12 18 24 48 72

Co

nju

gati

on

fre

qu

ency

Mycelial age (Hours)


196

Figure 4.9 Effect of mycelial solid growth medium on intergeneric conjugation between E. coli

ET12567/pUZ8002/pJN100 and S. polyantibioticus SPRT. The data are presented as the mean

± SEM of three independent experiments of the number of S. polyantibioticus SPRT

exconjugants observed per 1 x 107 donor E. coli cells.

4.4.3 GENE DISRUPTION USING OPTIMIZED INTERGENERIC

CONJUGATION METHOD

In order to determine which NRPS A domain is involved in DPO biosynthesis, in addition to

testing the involvement of the genes encoding the phenylacetate-CoA ligase, thioesterase,

cinnamate-CoA ligase, D-lactate dehydrogenase and acyl-CoA synthetase (as well as the

putative NRPS Cy domain) in DPO synthesis, it was decided that all of these genes could be

knocked-out in S. polyantibioticus SPRT using the method of homologous recombination.

The shuttle vector, pOJ260, was genetically manipulated for use in the gene disruption

experiments. Briefly, fragments of the genes encoding the A domain, Cy domain,

phenylacetate-CoA ligase, thioesterase, cinnamate-CoA ligase, D-lactate dehydrogenase and

0.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

6.0E-06

7.0E-06

8.0E-06

9.0E-06

YEME + 20mM MgCl2

YEME + 10mM MgCl2

MS + 10mMMgCl2

MS + 20mMMgCl2

7H9 + 10mM MgCl2

7H9 + 20mM MgCl2

ISP4 + 10mM MgCl2

ISP4 + 20mM MgCl2

Co

nju

gati

on

fre

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ency


197

acyl-CoA synthetase were individually cloned into pOJ260 and transformed into E. coli

ET12567/pUZ8002 for use in subsequent intergeneric conjugation with S. polyantibioticus

SPRT using the optimized, strain-specific conjugation method described in section 4.4.2.2.

The gene disruption experiments were based on the premise that the plasmid, pOJ260, carrying

a homologous region to a gene in S. polyantibioticus SPRT, would integrate into the genome

by a single crossover event and thereby disrupt the target gene (Figure 4.10). It would then be

possible to infer the gene’s involvement in the production of DPO, should the mutant strain

lose the ability to produce DPO. In order to detect the production of DPO after each respective

gene knockout, DPO was extracted from the resulting mutants and subjected to bioautography

against M. aurum A+. A loss in the detection of activity of the extract against M. aurum A+

indicated a loss of production of DPO and thereby confirmed the gene’s involvement in DPO

biosynthesis.

Fragments of the A domains designated AD2, A18, A16, A28, A7 and A99, in addition to the

genes encoding the phenylacetate-CoA ligase (PAAK), the Cy domain (CYC), acyl-CoA

synthetase (ACY), D-lactate dehydrogenase (LAC), cinnamate-CoA ligase (CIN) and

thioesterase (THI), were PCR-amplified from the S. polyantibioticus SPRT genome and

individually cloned into pOJ260. The resulting plasmids were designated pOJAD2, pOJA18,

pOJA16, pOJA28, pOJA7, pOJPAAK, pOJCYC, pOJA99, pOJACY, pOJLAC, pOJCIN and

pOJTHI, and were individually transformed into E. coli ET12567/pUZ8002 and introduced

into S. polyantibioticus SPRT via intergeneric conjugation to yield the mutant strains S.

polyantibioticus ∆AD2, S. polyantibioticus ∆A18, S. polyantibioticus ∆A16, S.


polyantibioticus ∆CYC, S. polyantibioticus ∆A99, S. polyantibioticus ∆ACY, S.

polyantibioticus ∆LAC, S. polyantibioticus ∆CIN and S. polyantibioticus ∆THI, respectively.

The location of DNA fragments used to make knock-out constructs within the genes they target,

according to Figure 4.10, is provided in Appendix C.


198

Figure 4.10 Schematic diagram representing the strategy employed in the construction of a theoretical gene

A disruption mutant (A). Gene disruption was achieved by inactivation of the target gene via

single crossover homologous recombination. The horizontal black arrows represent the position

of the binding sites of the PCR primers that were designed to confirm the integration of the

plasmid DNA, carrying the target gene of interest, into the wild-type chromosome. GSP refers

to the gene specific primer, depending on which target gene had been integrated into the S.

polyantibioticus SPRT genome. The GSP primer was used in conjunction with either the

POJFWD or POJREV primer. The binding positions of the POJFWD and POJREV primers on

the recombinant pOJ260 plasmid before integration of the whole plasmid into the genome is

also depicted. The apramycin resistance gene is represented by the abbreviation, apr. The

nucleotide sequences of the regions represented by the vertical arrows is provided in Appendix

C for each knock-out construct. (B). The red line indicates the target gene that has been cloned

into the multiple cloning region of pOJ260 and the numbers indicate the exact binding positions

on the plasmid according to the pOJ260 plasmid map (Figure 4.3).


199

Confirmation of the integration of the vector carrying the target gene of interest into the genome

of each mutant strain was determined by PCR amplification across the junctions of each copy

of the mutant gene derived from homologous recombination using the POJFWD primer and

the respective reverse gene specific primer (Figure 4.11-4.12). Amplification using the forward

gene specific primer of interest and POJREV in combination also confirmed the integration of

the vector carrying the target gene of interest (data not shown). Due to the binding positions of

the POJFWD and POJREV primers, the amplified products were 72 bp longer than the

amplified product obtained using the gene specific primer set, when using the POJFWD primer

in combination with the respective reverse target gene specific primer and 97 bp longer using

the POJREV primer in combination with the forward target gene specific primer (Table 4.5).

Additionally, the full open reading frame of the acyl-CoA synthetase was PCR-amplified and

cloned into the plasmid vector pJN100 to generate pJNACY, which was transformed into E.

coli ET12567/pUZ8002 and introduced into S. polyantibioticus ∆ACY via intergeneric

conjugation in order to complement the acyl-CoA synthetase mutant strain, S. polyantibioticus

∆ACY.


200

Figure 4.11 Gel electrophoresis of PCR amplified A domains from S. polyantibioticus SPRT using the

POJFWD and A7R primer set. Lanes: 1- λ-PstI molecular marker, 2- A18 amplification product

from S. polyantibioticus ∆18 gDNA, 3- A28 amplification product from S. polyantibioticus ∆28

gDNA, 4- A16 amplification product from S. polyantibioticus ∆16 gDNA, 5- A99 amplification

product from S. polyantibioticus ∆99 gDNA, 6- A7 amplification product from S.

polyantibioticus ∆7 gDNA, 7- AD2 amplification product from S. polyantibioticus ∆AD2

gDNA.

11.54

5.08

2.84

1.70

0.81

0.55

kb

1.16

1 2 3 4 5 6 7


201

Figure 4.12 Gel electrophoresis of PCR amplified target genes from S. polyantibioticus SPRT using the

POJFWD and reverse gene specific primers in combination. Lanes: 1- λ-PstI molecular marker,

2- CIN amplification product from S. polyantibioticus ∆CIN gDNA, 3- LAC amplifcation

product from S. polyantibioticus ∆LAC gDNA, 4- CYC amplification product from S.

polyantibioticus ∆CYC gDNA, 5- PAAK amplification product from S. polyantibioticus

∆PAAK gDNA, 6- THI amplification product, from S. polyantibioticus ∆THI gDNA.

11.54

5.08

2.84

1.70

0.81

0.55

kb

1.16

1 2 3 4 5 6


202

Table 4.5 PCR amplification product sizes of target genes using POJFWD and POJREV

primers Target gene Product size using POJFWD

and gene specific reverse primer

(bp)

Product size using gene specific

forward primer and POJREV

(bp)

A18 742 767

A16 771 796

A28 780 805

AD2 794 817

A7 802 827

A99 792 817

CIN 721 746

LAC 680 705

THI 545 570

CYC 1052 1149

PAAK 588 613

ACY 993 1017

4.4.4 ISOLATION OF DPO FROM S. POLYANTIBIOTICUS SPRT AND

CONFIRMATION OF ITS ACTIVITY AGAINST M. AURUM A+

The antibacterial compound, DPO, was isolated from the fermentation broth and mycelial mass

of S. polyantibioticus SPRT. The activity of the compound was detected through

bioautography, displaying an Rf of 0.88 with M. aurum A+ as the test organism.

Chemically-synthesized 2,5-diphenyloxazole was used as a positive control for the detection

of the bioactivity and its Rf value correlated with the biologically-produced compound (Figure

4.13). Furthermore, the solvent used in the purification of DPO, toluene, was employed as a

negative control in the detection of bioactivity in order to ensure that no contaminating

compounds with similar bioactivity to DPO were present.


203

Reverse-phase HPLC was employed to corroborate the results obtained from the bioautography

and the retention times measured at 280 nm of the biologically-produced DPO and chemically-

synthesized DPO were identical. The results of the TLC-bioautography analysis and reverse-

phase HPLC confirmed the production of DPO by S. polyantibioticus SPRT and its activity

against M. aurum A+.

Figure 4.13 TLC bioautography and RP-HPLC analysis of the biologically-synthesized DPO sample

isolated from S. polyantibioticus SPRT and the chemically synthesized DPO sample. (A) TLC

plates stained with MTT showing that both 1) the chemically synthesized DPO sample and 2)

the biologically-synthesized DPO sample had antibacterial activity and an Rf of 0.88 in the

solvent system used (100% ethyl acetate). (B) RP-HPLC analysis depicting the retention time,

29.65 min, of the chemically synthesized DPO sample measured at 280 nm. (C) RP-HPLC

analysis depicting the retention time, 29.65 min, of the biologically-synthesized DPO sample

measured at 280 nm.


204

4.4.5 TLC BIOAUTOGRAPHY ANALYSIS TO DETERMINE THE PUTATIVE

INVOLVEMENT OF THE TARGET GENES IN DPO BIOSYNTHESIS

In order to directly determine whether the A domains designated AD2, A18, A16, A28, A7 and

A99, as well as the genes encoding the phenylacetate-CoA ligase (PAAK), the Cy domain

(CYC), acyl-CoA synthetase (ACY), D-lactate dehydrogenase (LAC), cinnamate-CoA ligase

(CIN) and thioesterase (THI), are involved in the biosynthesis of DPO, each gene was disrupted

and the resulting mutant strain, lacking a functional copy of the target gene, was assayed for

activity against M. aurum A+. A loss in activity would suggest the gene’s involvement in DPO

biosynthesis.

The DPO purification method was carried out on cultures of strains S. polyantibioticus SPRT,

S. polyantibioticus ∆AD2, S. polyantibioticus ∆A18, S. polyantibioticus ∆A16, S.


polyantibioticus ∆CYC, S. polyantibioticus ∆A99, S. polyantibioticus ∆ACY, S.

polyantibioticus ∆LAC, S. polyantibioticus ∆CIN and S. polyantibioticus ∆THI. Each sample

was subjected to UV spectrophotometry which confirmed the presence of a single peak at a

wavelength of 280 nm in the samples from S. polyantibioticus SPRT, S. polyantibioticus ∆AD2,

S. polyantibioticus ∆A18, S. polyantibioticus ∆A16, S. polyantibioticus ∆A28, S.

polyantibioticus ∆A7, S. polyantibioticus ∆PAAK, S. polyantibioticus ∆LAC, S.

polyantibioticus ∆CIN and S. polyantibioticus ∆THI. In contrast, the samples from strains S.

polyantibioticus ∆CYC, S. polyantibioticus ∆A99 and S. polyantibioticus ∆ACY displayed a

reading of zero at a wavelength of 280 nm, thereby indicating that these strains had lost the

ability to produce DPO.

TLC-bioautography analysis was performed on the extracts from each strain, which showed

that S. polyantibioticus ∆AD2, S. polyantibioticus ∆A18, S. polyantibioticus ∆A16, S.


polyantibioticus ∆LAC, S. polyantibioticus ∆CIN and S. polyantibioticus ∆THI all had activity

against M. aurum A+ (Figures 4.14 and 4.15). This showed that disruption of these genes did

not abolish DPO production, which indicated that none of these genes is involved in DPO

biosynthesis. However, the extracts from strains S. polyantibioticus ∆CYC (Figure 4.16), S.

polyantibioticus ∆A99 (Figure 4.17) and S. polyantibioticus ∆ACY (Figure 4.18) showed no


205

activity against M. aurum A+, implying that the disruption of these genes resulted in the strains

losing the ability to produce DPO.

Figure 4.14 TLC plates stained with MTT showing the bioautographic analysis of DPO isolated from lane

B) S. polyantibioticus ∆AD2, lane C) S. polyantibioticus ∆A18, lane D) S. polyantibioticus

∆A16, lane E) S. polyantibioticus ∆A28 and lane F) S. polyantibioticus ∆A7, where lane A) is

chemically-synthesized DPO acting as a positive control.

Additionally, the introduction of pJNACY into S. polyantibioticus ∆ACY via intergeneric

conjugation in a complementation experiment, resulted in the restoration of DPO biosynthesis

and the ability to inhibit M. aurum A+ (Figure 4.18).

These results demonstrated the involvement of the Cy domain encoded by gene SPR_53040,

the A domain encoded by gene SPR_53060 and the acyl-CoA synthetase encoded by gene

SPR_52860 in the production of DPO. Furthermore, these results excluded the involvement

of the cinnamate-CoA ligase encoded by gene SPR_60150, the putative D-lactate

dehydrogenase encoded by gene SPR_60250 and the TE domain encoded by gene SPR_53090

A B C D E F


206

in the biosynthesis of benzoic acid, which is proposed to be required for DPO biosynthesis. It

also showed that none of the other A domains investigated is involved in DPO biosynthesis.


B) S. polyantibioticus ∆PAAK, lane C) S. polyantibioticus ∆LAC, lane E) S. polyantibioticus

∆CIN and lane F) S. polyantibioticus ∆THI, where lanes A) and D) are chemically-synthesized

DPO acting as a positive control.

A B C D E F


207


B) S. polyantibioticus SPRT, lane C) S. polyantibioticus ∆CYC, where lane A) is chemically-

synthesized DPO acting as a positive control.

A B C


208


B) S. polyantibioticus SPRT, lane C) S. polyantibioticus ∆A99, where lane A) is chemically-

synthesized DPO acting as a positive control.

A B C


209


B) S. polyantibioticus ∆ACY, lane C) S. polyantibioticus SPRT and lane D) S. polyantibioticus

PJNACY, where lane A) is chemically-synthesized DPO acting as a positive control.

A B C D


210

4.5 CONCLUSION An effective intergeneric conjugation method for the introduction of plasmid DNA from E. coli

ET12567 into S. polyantibioticus SPRT was developed and optimized. This method of

transformation allowed for the identification and targeted manipulation of the biosynthetic

pathway involved in DPO production. S. polyantibioticus mutant strains lacking a functional

copy of the putative Cy domain encoded by gene SPR_53040, the A domain encoded by gene

SPR_53060 and the acyl-CoA synthetase encoded by gene SPR_52860 exhibited a loss in the

production of DPO and were thereby identified as putative members of the DPO biosynthetic

pathway.

Due to the fact a gene encoding an acyl-CoA synthetase was not part of the initial hypothesis

on how DPO is produced, it was deemed necessary to amend the original theory. The

introduction of the revised hypothesis on how DPO is produced by S. polyantibioticus SPRT,

including an hypothesis on how benzoic acid is synthesized, is described in the following

chapter.


211

4.6 REFERENCE LIST Bailey, C.R. & Winstanley, D.J. (1986). Inhibition of restriction in Streptomyces clavuligerus by heat treatment.

Journal of General Microbiology, 132: 2945-2947.

Begg, K.J., Dewar, S.J. & Donachie, W.D. (1995). A new Escherichia coli cell division gene, ftsK. Journal of

Bacteriology, 177: 6211–6222.

Bibb, M.J., Ward, J.M. & Hopwood, D.A. (1978). Transformation of plasmid DNA into Streptomyces at high

frequency. Nature, 274: 398-400.

Bierman, M., Logan, R., O’ Brien, K., Seno, E.T., Rao, R.N. & Schoner, B.E. (1992). Plasmid cloning vectors

for the conjugal transfer of DNA from Escherichia coli to Streptomyces spp. Gene, 116: 43-49.

Bourn, W.R., Jansen, Y., Stutz, H., Warren, R.M., Williamson, A. & van Helden, P.D. (2007). Creation and

characterisation of a high-copy-number version of the pAL5000 mycobacterial replicon. Tuberculosis, 87: 481-

488.

Choi, S.U., Lee, C.K., Hwang, Y.I., Kinoshita, H. & Nihira, T. (2004). Intergeneric conjugal transfer of plasmid

DNA from Escherichia coli to Kitasatospora setae, a bafilomycin B1 producer. Archives of Microbiology, 181:

294–298.

Dagert, M. & Ehrlich, S.D. (1979). Prolonged incubation in calcium chloride improves the competence of

Escherichia coli cells. Gene, 6: 23-28.

Du, L., Liu, R. & Zhao, G. (2012). An efficient intergeneric conjugation of DNA from Escherichia coli to

mycelia of the lincomycin-producer Streptomyces lincolnensis. International Journal of Molecular Sciences, 13:

4797-4806.

Flett, F., Mersinias, V. & Smith, C.P. (1997). High efficiency intergeneric conjugal transfer of plasmid DNA

from Escherichia coli to methyl DNA-restricting streptomycetes. FEMS Microbiology Letters, 155: 223–229.

Frost, L.S., Ippen-Ihler, K. & Skurray, R.A. (1994). Analysis of the sequence and gene products of the transfer

region of the F sex factor. Microbiological reviews, 58(2): 162-216.

Giebelhaus, L., Frost, L., Lanka, E., Gormley, E.P., Davies, J.E. & Leskiw, B. (1996). The Tra2 core of the

InPα plasmid RP4 is required for intergeneric mating between Escherichia coli and Streptomyces lividans. Journal

of Bacteriology, 178(21): 6378-6381.


212

Gormley, E.P. & Davies, J. (1991). Transfer of plasmid RSF1010 by conjugation from Escherichia coli to

Streptomyces lividans and Mycobacterium smegmatis. Journal of Bacteriology, 173: 6705-6708.

Grohmann, E., Muth, G. & Espinosa, M. (2003). Conjugative plasmid transfer in gram-positive bacteria.

Microbiology and Molecular Biology Reviews, 67(2): 277-301.

Guan, D. & Pettis, G.S. (2009). Intergeneric conjugal gene transfer from Escherichia coli to the sweet potato

pathogen Streptomyces ipomoeae. Letters in Applied Microbiology, 49: 67–72.

Hacène, H. & Lefebvre, G. (1995). AH17, a new non-polyenic antifungal antibiotic produced by a strain of

Spirillospora. Microbios, 83: 199 - 205.

Heinzelmann E., Berger, S., Puk, O., Reichenstein, B., Wohlleben, W. & Schwartz, D. (2003). A glutamate

mutase is involved in the biosynthesis of the lipopeptide antibiotic friulimicin in Actinoplanes friuliensis.

Antimicrobial Agents and Chemotherapy, 47(2): 447-457.

Holo, H. & Nes, I.F. (1989). High-Frequency Transformation, by Electroporation, of Lactococcus

lactissubsp. cremoris Grown with Glycine in Osmotically Stabilized Media. Applied Environmental

Microbiology, 55(12): 3119–3123.

Hopwood, D.A. (1989). Antibiotics: opportunities for genetic manipulation. Philosophical Transactions of the

Royal Society B, 324: 549-562.

Hopwood, D.A., Kieser, T. (1993). Conjugative plasmids of Streptomyces. In Bacterial Conjugation. Clewell,

D.B. (ed.). New York: Plenum Press, 293–311.

Hussain, H.A., Ritchie, D.A. (1991). High frequency transformation of Streptomyces niveus protoplasts by

plasmid DNA. Journal of Applied Bacteriology, 71: 422-427.

Kieser, T., Bibb, M.J., Buttner, M.J., Chater, K. & Hopwood, D.A. (2000). Practical Streptomyces Genetics.

The John Innes Foundation: Norwich, UK.

Kieser, T. & Hopwood, D.A. (1991). Genetic manipulation of Streptomyces: integrating vectors and gene

replacement. Methods in Enzymology, 204: 430–458.

Kim, M.K., Ha, H.S. & Choi, S.U. (2008). Conjugal transfer using the bacteriophage phi C31 att/int system and

properties of the attB site in Streptomyces ambofaciens. Biotechnology Letters, 30: 695–699.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Heinzelmann%20E%5BAuthor%5D&cauthor=true&cauthor_uid=12543643

http://www.ncbi.nlm.nih.gov/pubmed/?term=Berger%20S%5BAuthor%5D&cauthor=true&cauthor_uid=12543643

http://www.ncbi.nlm.nih.gov/pubmed/?term=Puk%20O%5BAuthor%5D&cauthor=true&cauthor_uid=12543643

http://www.ncbi.nlm.nih.gov/pubmed/?term=Reichenstein%20B%5BAuthor%5D&cauthor=true&cauthor_uid=12543643

http://www.ncbi.nlm.nih.gov/pubmed/?term=Wohlleben%20W%5BAuthor%5D&cauthor=true&cauthor_uid=12543643

http://www.ncbi.nlm.nih.gov/pubmed/?term=Schwartz%20D%5BAuthor%5D&cauthor=true&cauthor_uid=12543643

http://aac.asm.org/


213

Kitani, S., Bibb, M.J. & Nihira, T. (2000). Conjugal transfer of plasmid DNA from Escherichia coli to

Streptomyces lavendulae FRI-5. Journal of Microbiology and Biotechnology, 10: 535–538.

Lacks, S., & Greenberg, B. (1977). Complementary specificity of restriction endonucleases of Diplococcus

pneumoniae with respect to DNA methylation. Journal of Molecular Biology, 114: 153-168.

Lanka, E. & Wilkins, B.M. (1995). DNA processing reactions in bacterial conjugation. Annual Review of

Biochemistry, 64: 141-169.

Lederberg, J. & Tatum, E.L. (1946). Gene recombination in Escherichia coli. Nature, 158: 558.

Le Roes, M. (2005). Selective isolation characterization and screening of actinomycetes for novel anti-tubercular

antibiotics. Ph.D. Thesis, Department of Molecular and Cell Biology, University of Cape Town. Chapter 5, 167-

182.

Luo, J.M., Li, J.S., Wang, Y.T., Luo, S.H. & Wang, M. (2009). Protoplast Formation and Regeneration

Conditions of Streptomyces gilvosporeus. In Proceedings of 2009 3rd International Conference on Bioinformatics

and Biomedical Engineering, Beijing, China, 11–13 June 2009; IEEE: Piscataway, NJ, USA: 1647–1650.

Ma, Z., Liu, J., Shentu, X., Bian, Y. & Yu, X. (2013). Optimization of electroporation conditions for

toyocamycin producer Streptomyces diastatochromogenes 1628. Journal of Basic Microbiology, 00: 1–7.

MacNeil, D.J., Gewain, K.M., Ruby, C.L., Dezeny, G., Gibbons, P.H. & MacNeil, T. (1992). Analysis of

Streptomyces avermitilis genes required for avermectin biosynthesis utilizing a novel integration vector. Gene,

111: 61-68.

MacNeil, D.J. (1988). Characterization of a Unique Methyl-Specific Restriction System in Streptomyces

avermitilis. Journal of Bacteriology, 170(12): 5607-5612.

Marcone, G.L., Carrano, L., Marinelli, F. & Beltrametti, F. (2010). Protoplast preparation and reversion to

the normal filamentous growth in antibiotic-producing uncommon actinomycetes. The Journal of Antibiotics, 63:

83-88.

Matshushima, P. & Baltz, R.H. (1985). Efficient plasmid transformation of Streptomyces ambofaciens and

Streptomyces fradiae protoplasts. Journal of Bacteriology, 163: 180-185.

Matshushima, P., Broughton, M.C., Turner, J.R. & Baltz, R.H. (1994). Conjugal transfer of cosmid DNA

from Escherichia coli to Saccharopolyspora spinosa: effects of chromosomal insertions on macrolide A83543

production. Gene, 146: 39-45.


214

Mazodier, P. & Davies, J. (1991). Gene transfer between distantly related bacteria. Annual Review of Genetics,

25: 147-171.

Mazodier, P., Petter, R. & Thompson, C. (1989). Intergeneric conjugation between Escherichia coli and

Streptomyces species. Journal of Bacteriology, 171: 3583-3585.

Mazy-Servais, C., Backowski, D. & Dusart, J. (1997). Electroporation of intact cells of Streptomyces parvulus

and Streptomyces vinaceus. FEMS Microbiology letters, 151: 135-138.

McDonald, I.R., Riley, P.W., Sharp, R.J. & McCarthy, A.J. (1995). Factors affecting the electroporation of

Bacillus subtilis. Journal of Applied Bacteriology, 79(2): 213-218.

Nikodinovic, J. & Priestley, N.D. (2006). A second generation snp-derived Escherichia coli-Streptomyces

shuttle expression vector that is generally transferable by conjugation. Plasmid, 56: 223-227.

Okanishi, M., Suzuki, K. & Umezawa, H. (1974). Formation and reversion of streptomycete protoplasts: cultural

conditions and morphological study. Journal of General Microbiology, 80:389-400.

Paget, M. S. B., Chamberlin, L., Atrih, A., Foster, S. J. & Buttner, M. J. (1999). Evidence that the

extracytoplasmic function sigma factor sigma E is required 95 for normal cell wall structure in Streptomyces

coelicolor A3(2). Journal of Bacteriology, 96(181): 204-211.

Papagianni, M., Avramidis, N. & Filioussis, G.. (2007). High efficiency electrotransformation of Lactococcus

lactisspp. lactis cells pretreated with lithium acetate and dithiothreitol. BMC Biotechnology, 7: 15-23.

Paranthaman, S. & Dharmalingam, K. (2003). Intergeneric conjugation in Streptomyces peucetius and

Streptomyces sp. strain C5: Chromosomal integration and expression of recombinant plasmids carrying the chiC

gene. Applied Environmental Microbiology, 69: 84–91.

Pigac, J. & Schrempf, H. (1995). A simple and rapid method of transformation of Streptomyces rimosus R6 and

other streptomycetes by electroporation. Applied Environmental Microbiology, 61:352-356.

Possoz, C., Ribard, C., Gagnat, J., Pernodet, J.L. & Guerineau, M. (2001). The integrative element pSAM2

from Streptomyces: kinetics and mode of conjugal transfer. Molecular Microbiology, 42: 159–166.

Raleigh, E. A., & Wilson, G. (1986). Escherichia coli K-12 restricts DNA containing 5-methylcytosine. Proceedings of the National Academy of Sciences USA, 83: 9070-9074.


215

Sambrook, J., Fritsch, E.F. & Maniatis, T. (1989). Bacterial media, antibiotics and bacterial strains. Molecular

Cloning, a laboratory manual, 2nd Ed. Cold Spring Harbour: Cold Spring Harbour Laboratory Press.

Sanger, F., Nicklen, S. & Coulson, A., R. (1977). DNA Sequencing with chain-terminating inhibitors.

Biotechnology. 24: 104-108.

Shigekawa, K. & Dower, W.J. (1988). Electroporation of eukaryotes and prokaryotes: a general approach to the

introduction of macromolecules into cells. Biotechniques, 6(8):742-751.

Shirling, E. B. & Gottlieb, D. (1966). Methods for characterization of Streptomyces species. International

Journal of Systematic Bacteriology, 16: 313-340.

Simon, R., Priefer, U. & Puhler, A. (1983). A broad host range mobilisation system for in vivo genetic

engineering: transposon mutagenesis in Gram-negative bacteria. Biology/Technology, 1: 784-791.

Spath, K., Heinl, S. & Grabherr, R. (2012). Direct cloning in Lactobacillus plantarum: Electroporation with

non-methylated plasmid DNA enhances transformation efficiency and makes shuttle vectors obsolete. Microbial

Cell Factories, 11:141-147.

Stegmann, E., Pelzer, S., Wilken, K. & Wohlleben, W. (2001). Development of three different gene cloning

systems for genetic investigation of the new species Amycolatopsis japonicum MG417-CF17, the

ethylenediaminedisuccinic acid producer. Journal of Biotechnology, 92: 195-204.

Sunairi, M., Iwabuchi, N., Murakami, K., Watanabe, F., Ogawa, Y., Murooka, H. & Nakajima, M. (1996).

Effect of penicillin G on the electroporation of Rhodococcus rhodochrous CF222. Letters in Applied

Microbiology, 22(1): 66-69.

Trieu-Cuot, P., Carlier, C., Martin, P. & Courvalin, P. (1987). Plasmid transfer by conjugation

from Escherichia coli to Gram-positive bacteria. FEMS Microbiology Letters, 48: 289-294.

Tyurin, M., Starodubtseva, L., Kudryavtseva, H., Voeykova, T. & Livshits, V. (1995). Electrotransformation

of germinating spores of Streptomyces spp. Biotechnology techniques, 9: 737-740.

Vasu, K. & Nagaraja, V. (2013). Diverse Functions of Restriction-Modification Systems in Addition to Cellular

Defense. Microbiology and Molecular Biology Reviews, 77(1): 53-72.

Voeikova, T.A. (1999). The conjugal transfer of plasmids from Escherichia coli to various strains of the order

Actinomycetales. Russian Journal of Genetics, 35(12): 1398-1404.

http://mmbr.asm.org/search?author1=Kommireddy+Vasu&sortspec=date&submit=Submit

http://mmbr.asm.org/search?author1=Valakunja+Nagaraja&sortspec=date&submit=Submit

http://serials.unibo.it/cgi-ser/start/en/spogli/df-s.tcl?prog_art=6895982&language=ENGLISH&view=articoli

http://serials.unibo.it/cgi-ser/start/en/spogli/df-s.tcl?prog_art=6895982&language=ENGLISH&view=articoli


216

Vollmer, W. (2008). Structural variation in the glycan strands of bacterial peptidoglycan. FEMS microbiology

reviews, 32(2): 287-306.

Wilkinson, C.J., Hughes-Thomas, Z.A., Martin, C.J., Bohm, I., Mironenko, T., Deacon, M., Wheatcroft,

M., Wirtz, G., Staunton, J. & Leadlay, P.F. (2002). Increasing the Efficiency of Heterologous Promoters in

Actinomycetes. Journal of Molecular Microbiology and Biotechnology, 4(4): 417–426.

Willetts, N. & Wilkins, B.M (1984). Processing of plasmid DNA during bacterial conjugation. Microbiology

Review, 48(1): 24-41.

Wu, L.J., Lewis, P.J., Allmansberger, R., Hauser, P.M. & Errington, J. (1995). A conjugation-like mechanism

for prespore chromosome partitioning during sporulation in Bacillus subtilis. Genes Development, 9: 1316–1326.

Yanisch-Perron, C., Vieira J. & Messing J. (1985). Improved M13 phage cloning vectors and host strains:

nucleotide sequences of the M13mp18 and pUC19 vectors. Gene, 33: 103-119.

Zhang, H.Z., Schmidt, H. & Piepersberg, W. (1992). Molecular cloning and characterization of two

lincomycin-resistance genes, lmrA and lmrB, from Streptomyces lincolnensls 78-11. Molecular Microbiology, 6:

2147–2157.

Zhang, P., Xu, P., Wang, J., Xiong, J. & Li, Y. (2013). Combined treatment with the antibiotics kanamycin

and streptomycin promotes the conjugation of Escherichia coli. FEMS Microbiology Letters, 348(2): 149-156.

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CHAPTER 5

GENERAL DISCUSSION

218

CHAPTER 5

GENERAL DISCUSSION

5.1 Introduction ................................................................................................................ 219

5.2 Identification and characterisation of the genes involved in joining benzoic acid and

phenylalanine/3-hydroxyphenylalanine in S. polyantibioticus SPRT to create a 2,5-

disubstituted oxazole ................................................................................................. 221

5.3 Identification of the genes responsible for the biosynthesis of benzoic acid in

S. polyantibioticus SPRT ........................................................................................... 228

5.4 Proposed pathway for the biosynthesis of DPO in S. polyantibioticus SPRT ........... 237

5.5 Conclusion and future work ....................................................................................... 240

5.6 Reference list ............................................................................................................. 241

Chapter 5 – General Discussion

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CHAPTER 5

GENERAL DISCUSSION

5.1 Introduction

Natural products, such as bacterial secondary metabolites, have proven to be valuable sources

of novel compounds exhibiting a diverse array of biological activities. Indeed, due to their

diverse and complex chemical structures, bacterial secondary metabolites have demonstrated

their use as pharmacologically active compounds that continue to serve medicine well by

offering novel leads for novel therapeutic agents (Harvey, 1999; Bernan et al., 1997).

Additionally, the great structural and chemical diversity of natural products makes them well-

suited for manipulation by chemical and/or genetic means to generate semi-synthetic drugs

with improved antimicrobial and pharmacological properties (Ashforth et al., 2010). The first-

line anti-TB drug, rifampicin, for example, was developed from the rifamycins, which are

produced by members of the actinobacterial genus, Amycolatopsis (Wright, 2012).

The need for novel antibiotics with novel mechanisms of action has become urgent with the

increased occurrence of bacterial resistance to known antibiotics and the emergence of new

and old diseases (especially in the case of tuberculosis) (Bérdy, 2005).

It has been estimated that only 1–3 % of all antibiotics have been discovered, meaning that

there is a high likelihood of identifying new antibiotic molecules from bacteria (and particularly

actinobacteria) through a taxonomy-guided exploration of bacterial biodiversity. Certainly, the

bacteria belonging to the suborders Streptomycineae (e.g. Streptomyces), Micromonosporineae

(e.g. Micromonospora), Pseudonocardineae (e.g. Amycolatopsis) and Streptosporangineae

(e.g. Planobispora) (all in the order Actinomycetales; class Actinobacteria) are the most

prolific producers of novel antimicrobial antibiotics (Ashforth et al., 2010). To gain access to

the biodiversity in these (and other) actinobacterial suborders, it is important to isolate


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actinobacteria from many different environments, e.g. terrestrial soil and marine sediments, as

well as from plants and animals.

Actinobacterial genomes (particularly those of the actinomycetes, such as Streptomyces) are

larger than those of most other bacteria, possessing a high capacity for the synthesis of

secondary metabolites and employing a substantial fraction of coding capacity (5–10 %) for

the production of mostly cryptic secondary metabolites (Baltz, 2008). The sequenced

actinobacterial genomes are a valuable resource, which have revealed that actinobacteria have

the biosynthetic potential to make far more natural products than was realised (Ashforth et al.,

2010). The taxonomic diversity covered by these sequenced genomes has revealed that the

more bacterial genomes that are sequenced, the more new gene families are discovered (Wu et

al., 2009). Thus, identifying taxonomic diversity reveals new genetic diversity and therefore

new biosynthetic capabilities.

In light of the taxonomy-guided bacterial bioprospecting approach described above,

S. polyantibioticus SPRT was isolated as part of an antibiotic-screening programme and

identified as the producer of several antibiotics (Le Roes-Hill & Meyers, 2009; Le Roes, 2005).

One of these antibiotics possessed antitubercular activity and was identified as DPO (Le Roes,

2005). In this study, the S. polyantibioticus SPRT genome was sequenced and explored in order

to identify the biosynthetic pathway involved in DPO biosynthesis and thereby take the first

step towards the generation of derivatives of DPO by combinatorial biosynthesis.

Combinatorial biosynthesis is a powerful way to generate antibiotic derivatives with greater

antibacterial activity and/or improved pharmacokinetic properties. It has advantages over the

chemical derivatisation of antibiotic molecules, since the bacterial biosynthetic enzymes carry

out site-specific and enantiomer-specific reactions, by-passing the need to protect reactive

functional groups in each reaction step in the chemical approach. This ensures that only the

desired product is produced, which enhances the product yield.

In order to determine whether the proposed biosynthetic pathway is correct, the genes coding

for benzoic acid synthesis and the DPO NRPS had to be identified in the S. polyantibioticus

SPRT genome. The research aims of this study, as described in Chapter 1, are discussed in the

following sections within the context of the original hypothesis for DPO biosynthesis in S.



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5.2 Identification and characterisation of the genes involved in joining

benzoic acid and phenylalanine/3-hydroxyphenylalanine in S.

polyantibioticus SPRT to create a 2,5-disubstituted oxazole

Based on the structure of DPO, a biosynthetic scheme for the synthesis of this molecule, in

which an NRPS condenses a molecule of benzoic acid with 3-hydroxyphenylalanine (also

known as 3-phenylserine) to form an amide bond between them, was proposed (Chapter 1).

This intermediate, known as N-benzoyl-β-hydroxyphenylalanine (Figure 5.1), is subsequently

converted to a diphenyloxazole derivative by heterocyclization across the amide bond, after

which a final decarboxylation step leads to DPO. An NRPS is believed to be the core enzyme

in the synthesis of DPO due to the presence of an oxazole in the DPO structure.

Figure 5.1 The proposed amide-bond-containing precursor to DPO, N-benzoyl-β-hydroxyphenylalanine.

The atoms joined by the three red bonds (i.e. running from the carbonyl C atom of benzoic acid

to the hydroxyl C atom of 3-hydroxyphenylalanine) are involved in forming a 5-membered

heterocyclic ring, i.e. an oxazole.

Initial efforts to isolate and identify the DPO biosynthetic gene cluster in S. polyantibioticus

SPRT identified twelve unique NRPS A domains. The specificities of these A domains were

identified using NRPSpredictor2 (Rausch et al., 2005). This approach has been used in

numerous studies and is considered accurate. However, there have been examples of substrate-


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specificity codes for which the predicted substrate specificity does not correspond to the

activated amino acid identified in vivo (Lombó et al., 2006). A study by McQuade et al. (2009)

suggested that, in addition to the 10 key residues of the binding pocket, there may be other

residues involved in controlling the substrate amino acid activated by an A domain.

In this study, the A domain contained within the inserts of the identical clones pGEMA-18 and

pGEMA-66 was predicted to be specific for the activation of phenylalanine, while two A

domains contained within the inserts of the clones pGEMA-5/pGEMA-7/pGEMA-

12/pGEMA-22 and pGEMA-36/pGEMA-51/pGEMA-63, where predicted to be specific for

serine. Serine is a common starter unit for the biosynthesis of oxazoles. However, if serine

were used in DPO biosynthesis, it would require the addition of a phenyl group to the oxazole

structure (Roy et al., 1999). Importantly, β-phenylation of an activated serine has not yet been

reported to occur in bacteria and it therefore seems more likely that β-hydroxylation of an

activated phenylalanine residue by a P450 monooxygenase would be the mechanism involved

in DPO biosynthesis. Nevertheless, it is possible that a β-phenylation reaction is used by S.

polyantibioticus SPRT (Le Roes, 2005).

Annotation of the S. polyantibioticus SPRT draft genome sequence revealed that the A domain

insert in clone pGEMA-18/pGEMA-66 is encoded by gene SPR_48330. This gene was

predicted by antiSMASH 3.0 to be involved in the biosynthesis of an antimycin-type antibiotic

and was therefore dismissed as being a member of the DPO biosynthetic cluster. Similarly,

the A domains predicted to activate serine and contained within the clones pGEMA-5/pGEMA-

7/pGEMA-12/pGEMA-22 and pGEMA-36/pGEMA-51/pGEMA-63, are encoded by the genes

SPR_56140 and SPR_56150, respectively. Due to their predicted involvement in the

biosynthesis of a complex PKS/NRPS hybrid secondary metabolite, genes SPR_56140 and

SPR_56150 were deemed unlikely to be involved in DPO biosynthesis. Nevertheless, the A

domains designated A-7 and A-18 (Chapter 2), in addition to the AD-2, A-16 and A-28

domains encoded by the genes SPR_6340, SPR_28920 and SPR_6040, respectively, were

disrupted by homologous recombination in S. polyantibioticus SPRT. Subsequent

bioautography experiments confirmed that genes SPR_6340, SPR_28920 and SPR_6040 are

not involved in DPO biosynthesis, as inactivation of these genes did not abolish DPO

production by the mutant strains.


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Conversely, the A domain, A-99, encoded by SPR_53060 was confirmed as a putative member

of the S. polyantibioticus SPRT DPO biosynthetic pathway due to the fact that an

S. polyantibioticus mutant strain lacking a functional copy of this A domain exhibited a loss of

production of DPO. The specificity prediction of this A domain was however inconclusive, as

the software tools predicted specificity for both phenylalanine and tryptophan (Chapter 3).

Nevertheless, the relaxed substrate specificity of the A domains in xenematide A biosynthesis

has demonstrated the ability of A domains for aromatic amino acids to accept either tryptophan

or phenylalanine as substrates. Furthermore, Schaffer & Otten (2009) demonstrated in the

tyrocidine A biosynthetic pathway that although A domains are selective for specific substrates,

many of these domains possess the ability to adenylate a number of different substrates. Thus,

the A domain encoded by SPR_53060 might accept phenylalanine or 3-hydroxyphenylalanine

as a substrate in the biosynthesis of DPO.

However, if 3-hydroxyphenylalanine is not the starter molecule in DPO biosynthesis, it is

possible that an alternative starter molecule such as 1-phenyl-2-aminoethanol could be used in

DPO biosynthesis (Figure 5.2). Indeed, 2-aminoethanol (ethanolamine) is a compound derived

from cell membranes that certain bacteria can utilize as a source of carbon and/or nitrogen

(Garsin, 2010). It is also possible that S. polyantibioticus SPRT could utilize glycine to

synthesize 2-aminoethanol by reduction of the carboxyl group. However, a phenylation

reaction would need to occur to generate 1-phenyl-2-aminoethanol.

It is evident that, due to the weak predictions of the software tools and the contradictory results,

the substrate specificity of the A domain encoded by SPR_53060 can only be elucidated by

experimental analysis. Due to the fact that A domains consume ATP and release PPi during

the activation of their substrates, and because the activation reaction is reversible, A domain

selectivity can be assayed using the conventional ATP-32PPi isotope exchange assay in vitro.

During this assay, the A domain of interest is incubated with the potential substrate, ATP, Mg2+

and 32P-labeled PPi. During the reverse activation reaction, 32P from the labeled PPi is

incorporated into ATP if the amino acid(s) present in the assay is/are activated by the A domain.

The 32P-ATP can then be separated via adsorption to activated charcoal. The amount of

generated 32P-ATP is proportional to the substrate activation reaction (Phelan et al., 2009;

Linne & Marahiel, 2004). However, Phelan et al. (2009) developed a non-radioactive mass

spectrometry (MS)-based PPi exchange assay that is able to measure the consumption of


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γ-18O4-labelled ATP and the formation of 16O4-ATP by the isotopic back exchange of excess

unlabelled PPi. The resulting mass shifts are detected by MALDI-TOF-MS and the activity of

the A domain can therefore be measured. Incubation with different substrates and a comparison

of each substrate’s ATP-PPi exchange rate allows for the determination of the substrate

specificity of the A domain under scrutiny. In contrast to the issues observed in the

conventional systems, this exchange assay provides a rapid, sensitive and reproducible means

to measure A domain specificity (Phelan et al., 2009). This technique has been used

successfully to determine the A domain specificity in studies of Streptomyces refuinius (Phelan

et al., 2009) and Streptomyces coeruleorubidus NRRL 18370 (Zhang et al., 2010), thereby

providing an alternative option for the substrate prediction of A domains in future studies of S.


Additionally, the A domain of the acyl-CoA synthetase encoded by SPR_52860 was predicted

to be specific for the activation of an aromatic substrate such as 2,3-dihydroxybenzoic acid (or

a derivative thereof), phenylalanine or tryptophan (Chapter 3). This gene was identified as a

member of the DPO biosynthetic pathway via the gene disruption and complementation

experiments described in Chapter 4.

The family of coenzyme A ligases includes the A domains of NRPSs, firefly luciferase and

acyl- and aryl-CoA synthetases, such as the acyl-CoA synthetase encoded by SPR_52860.

Reactions catalysed by this family of enzymes proceed in two steps in which the substrate

reacts with ATP to form an acyl-adenylate intermediate with the simultaneous release of

pyrophosphate. Thereafter, the adenylate group is replaced by CoA, accompanied by the

release of AMP (Gulick, 2009). The CoA-ligases are known to initiate β-oxidation via the

activation of fatty acids and are important in the biosynthesis of natural products such as the

penicillins (Koetsier et al., 2009) and lignin (Anterola & Lewis, 2002) (Figure 5.3).


225

Figure 5.2 Proposed alternative route to DPO biosynthesis in S. polyantibioticus SPRT. A molecule of

benzoic acid (A) is condensed with 1-phenyl-2-aminoethanol (B) to form an ester bond between

them. Subsequent heterocyclization and decarboxylation of the intermediate, O-benzoyl-1-

phenyl-2-aminoethanol (C), would lead to DPO (D).

As the acyl-CoA synthetase encoded by SPR_52860 was identified as a member of the DPO

biosynthetic pathway, it would activate its substrate, benzoic acid, as a CoA-thioester.

Thereafter, the first reaction in DPO biosynthesis would proceed via amide bond formation

between an aminoacyl-bound PCP-thioester and the CoA-thioester. Although the activation of

a Cy domain substrate as a CoA-thioester instead of a PCP-Ppant-thioester is unusual, it has

been reported in the biosynthesis of congocidine (Juguet et al., 2009), the calcium-dependent

antibiotics (Hojati et al., 2002) and fengycin (Steller et al., 1999). It is interesting to note that

the aspartate residue (D235 according to the GrsA-PheA numbering convention) that is


226

conserved in the majority of A domains and which is involved in the binding of the α-amino

acid substrate is replaced by a glycine in the substrate specificity binding pocket of the A

domain encoded by SPR_52860. It is therefore suggested that the substrate of the SPR_52860

A domain does not possess an α-amino group, which would support the hypothesis that an

aromatic acid, such as benzoic acid, is indeed activated.

Figure 5.3 Examples of reactions catalysed by members of the family of adenylate-forming enzymes. (A)

The activation of the pencillin G side chain phenylacetic acid is catalysed by a phenylacetate-

CoA ligase in Penicillium chrosygenum (adapted from Koetsier et al., 2011). (B) The activation

of benzoic acid for DPO biosynthesis is believed to be catalysed by an acyl CoA-synthetase in

S. polyantibioticus SPRT.

Although, in the initial experiments described in Chapter 2, a Cy domain could not be amplified

from the S. polyantibioticus SPRT genome, a phylogenetic analysis of all of the identified C

domains within the S. polyantibioticus SPRT draft genome provided insight into the degree of

evolutionary relatedness of these domains to well-characterised reference Cy domains. The

domains encoded by SPR_53060, SPR_53040, SPR_6230, SPR_6240 and SPR_6360 shared

the highest degree of evolutionary relatedness to the reference Cy domains and an analysis of

the conserved signature motifs within these domains identified SPR_53040 and SPR_53060 as

displaying an unusual putative tandem condensation/heterocyclization function in DPO

biosynthesis. This was deduced because SPR_53040 lacks the catalytic second aspartate


227

residue found in the Cy domain consensus motif, whereas SPR_53060 lacks the first Cy domain

aspartate residue.

It has been demonstrated that the second aspartate residue in the Cy domain motif D-x-x-x-x-

D-x-x-S motif is critical for catalytic Cy activity, however the role of the first aspartate is still

unclear. Mutation of the first aspartate residue to alanine resulted in the elimination of the

activity in the first Cy domain of the yersiniabactin synthetase subunit HMWP2, while a

comparable mutation in the Cy domain of the vibriobactin NRPS module VibF resulted in only

a 10-fold reduction in activity (Marshall et al., 2002; Keating et al., 2000). The significance

of the first aspartate residue of the consensus motif was also examined via an alanine mutation

in the NRPS subunit EntF of enterobactin synthetase, where activity was only diminished 2-

fold in comparison to the wild type strain. The authors surmised that this result implicates the

residue as critical but not essential for heterocycle formation, with its importance varying

according to the synthetase and substrate in question (Kelly et al., 2005).

The serine residue found in the D-x-x-x-x-D-x-x-S motif is not strictly conserved among Cy

domains and a mutation of the serine residue to alanine in the yersiniabactin synthetase subunit

HMWP2 Cy domain resulted in no effect on heterocycle formation. This suggests that the lack

of a serine residue in the signature motif found in the putative Cy domain encoded by

SPR_53040 is of limited significance (Keating et al., 2000).

Peptide bond formation and heterocyclization usually depend on the action of a single Cy

domain. However, a situation where these two reactions are split between two Cy domains

was observed in the biosynthesis of the oxazoline-containing siderophore vibriobactin in Vibrio

cholerae. Such a split-function Cy-domain pair is believed to be involved in the DPO

biosynthetic pathway. The NRPS responsible for the formation of vibriobactin consists of an

unusual Cy-Cy tandem arrangement, where the first domain is responsible for heterocyclization

and the second domain is responsible for condensation (Schwarzer et al., 2003; Marshall et al.,

2002).

Additionally, in the biosynthesis of holomycin by Streptomyces clavuligerus, a tridomain

module with the organization Cy-A-PCP, together with a lone C domain, are proposed to be

responsible for the selection, activation, heterocyclization and oxidation of two cysteine


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residues in the biosynthesis of the final product. This further demonstrates the flexibility of

NRPS systems, where instead of a Cy domain simply replacing the C domain as observed in

conventional NRPS elongation modules for oxazoles and thiazoles, a pair of domains functions

in tandem (Li & Walsh, 2010).

5.3 Identification of the genes responsible for the biosynthesis of benzoic

acid in S. polyantibioticus SPRT

In bacteria, only a handful of benzoic acid derived metabolites have been described, seemingly

due to the rarity of PAL in these organisms. Indeed, despite the plant-like biosynthesis of

benzoyl-CoA described in “S. maritmus” strain DSM 41777T, where this rare starter unit is

involved in the production of the structurally novel polyketide enterocin (Hertweck & Moore,

2000), unsubstituted benzoyl units have only been found in benzoyl α-L-rhamnopyranoside

produced by Streptomyces griseoviridis Tü 3634 (Hoffman & Grond, 2004), as well as in the

structures of aestivophoenin A (Kunigami et al., 1998) and wailupemycin (Hertweck & Moore,

2000), all isolated from Streptomyces spp., and in the myxobacterial molecules soraphen (Hill

et al., 2003), thiangazole and crocacin (Jansen et al., 1992). In stark contrast to this, the

occurrence of benzoyl units is common in secondary metabolites produced by plants and fungi,

such as in the cancer drug taxol (Rohr, 1997) and the fungicide strobilurin (Nerud et al., 1982).

In addition to the aerobic benzoyl-CoA biosynthetic process catalysed by PAL in “S. maritmus”

strain DSM 41777T, there is evidence for two PAL-independent pathways resulting in the

biosynthesis of benzoic acid, namely, via: 1) the anaerobic degradation of L-phenylalanine

described in the denitrifying bacterium Thauera aromatica (Breese et al., 1998; Schneider et

al., 1997) and 2) directly from shikimate (Hoffman & Grond, 2004). Additionally, soraphen

A biosynthesis in S. cellulosum is an example of an aerobic non-PAL pathway, which begins

with a phenyl side group that is derived from phenylalanine, but the exact pathway for the

generation of benzoic acid is unknown. It has been proposed that carboxybenzoyl-CoA is an

intermediate in the biosynthesis of benzoic acid in S. cellulosum (Schupp et al., 1995, Ligon et

al., 2002).

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC526270/#ref6




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In this study, a number of approaches to obtaining the genes responsible for the biosynthesis

of benzoic acid in S. polyantibioticus SPRT were explored. The first approach focused on the

search for an orthologue of the encP gene, which encodes PAL. Despite utilizing

‘S. maritimus’ DSM 41777T as a positive control, no encP orthologue was detected in the

S. polyantibioticus SPRT genome by PCR amplification and Southern blotting. However, a

HAL, which is highly homologous to PAL and catalyzes the analogous deamination of

histidine to trans-urocanate in prokaryotes, thereby initiating histidine degradation (Michal,

1999), was detected in the S. polyantibioticus SPRT genome using PCR amplification and

sequencing. Both HAL and PAL enzymes are also homologous to tyrosine ammonia lyase

(TAL), an enzyme commonly found in plants (Kyndt et al., 2002). All three enzymes contain

the unique prosthetic group 4-methylidene imidazol-5-one, which may indicate a similar

catalytic mechanism (Bode & Müller, 2003; Rother et al., 2001; Schwede et al., 1999). Due

to the fact that PAL is the first enzyme in the plant phenylpropanoid biosynthetic pathway, it

has received the greatest attention and is therefore the best studied member of this enzyme

family (Schuster & Retey, 1995). Since a PAL was not detected in the S. polyantibioticus SPRT

genome, an alternative pathway for the production of cinnamic acid was proposed whereby the

need for a PAL was bypassed (Chapter 3). This pathway was proposed on the basis of the

discovery of a cinnamate CoA ligase, encoded by SPR_60150, in the S. polyantibioticus SPRT

draft genome. SPR_60150 displayed significant homology to the enzyme, 4-coumarate-CoA

ligase (4CL, EC: 6.2.1.12), which has been characterized to occur in the biosynthetic route to

benzoyl-CoA in “S. maritmus” strain DSM 41777T. In addition, 4CL, which catalyzes the final

reaction of the phenylpropanoid pathway in plants, has also been characterized in S. coelicolor

A3(2) (Kaneko et al., 2003). Similarly to S. polyantibioticus SPRT, a PAL was not detected in

the S. coelicolor A3(2) genome. Therefore, if cinnamate or 4-coumarate are physiological

substrates, they may be supplied from dead plants in the environment, although no uptake

system for either of these compounds has been described in Streptomyces spp. (Kaneko et al.,

2003).

Three genes encoding a putative acetyl/propionyl-CoA carboxylase, a putative acyl-CoA

dehydrogenase and a putative enoyl-CoA hydratase exist in the immediate vicinity of the gene

encoding the 4CL enzyme in the genome of S. coelicolor A3(2) and, due to the fact that

functionally related genes are normally clustered in bacterial genomes, the authors speculated

that the 4CL, together with the enzymes encoded by the three other genes, are involved in the




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production of a secondary metabolite (Kaneko et al., 2003). In light of this and the fact that a

putative enoyl-CoA hydratase and a putative acyl-CoA dehydrogenase were found next to the

gene encoding a cinnamate-CoA ligase in the S. polyantibioticus SPRT genome, this cluster

was identified as being putatively responsible for the biosynthesis of benzoic acid.

The proposed pathway involved the catabolism of phenylalanine to cinnamic acid via

phenylpyruvate and phenyllactate (Chapter 3). The D-lactate dehydrogenase encoded by

SPR_60260 and the cinnamate CoA ligase encoded by SPR_60150 were disrupted and S.

polyantibioticus single mutant strains lacking a functional copy of each of these genes were

able to produce DPO, thereby proving that they are not involved in the DPO biosynthetic

pathway.

Thus, benzoic acid does not appear to be synthesized in S. polyantibioticus SPRT via a PAL-

dependant pathway or via another cinnamate-containing pathway in which the PAL reaction is

bypassed. As studies have demonstrated that antibiotic production in actinomycetes and other

microorganisms makes use of amino acids as precursors, such as in the biosynthesis of

oleandomycin in S. antibioticus, the second approach to determining the genes responsible for

benzoic acid biosynthesis focussed on a novel variation of the phenylacetate degradation

pathway (Tang et al., 1994). Phenylacetic acid (PA) is a common intermediate in the microbial

metabolism of a variety of aromatic substrates including phenylalanine but, although there are

examples of aerobic, non-PAL pathways in nature (often utilising PA as the starter unit), none

of them is fully understood.

In the denitrifying bacterium, Thauera aromatica, PA is catabolized under anoxic conditions

to benzoyl-CoA via the intermediates phenylacetyl-CoA and phenylglyoxylate (Rhee & Fuchs,

1999). This mechanism is similar to the pathway described in A. evansii, in which it is

speculated that an aerobic pathway may coexist in order to fully metabolise PA. Moreover, an

aerobic pathway for the degradation of PA has been established in Gram-negative bacteria such

as Pseudomonas putida and E. coli, whereby PA is first converted to PA-CoA, which

subsequently undergoes ring hydroxylation, hydrolytic-ring opening and further degradation.

In contrast, this pathway and its role have not been comprehensively characterised in Gram-

positive bacteria, although a study of Rhodococcus sp. strain RHA1 provided conclusive

evidence that it does have a functional PA degradation pathway that is partially responsible for


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the degradation of styrene, ethylbenzene and 3-hydroxyphenylacetate (Navarro-Llorens et al.,

2005). However, the existence of benzoic acid or benzoyl-CoA as a final product in these

aerobic pathways has yet to be established.

Furthermore, the PA catabolon has been described to be involved in the biosynthesis of the

seconday metabolite, antimycin A, produced by Streptomyces albus S4 (Seipke & Hutchings,

2013) and in the biosynthetic pathway for the production of neoantimycin, part of the antimycin

family of depsipeptides, by Streptoverticillium orinoci (Li et al., 2013).

In light of the fact that the PA catabolon has been associated with the production of secondary

metabolites and because a PA-CoA ligase is responsible for the catalysis of the first reaction in

this pathway, catalysing the activation of PA to PA-CoA, a homologue of the gene encoding

this enzyme, paaK, was amplified from the S. polyantibioticus SPRT genome. However, an S.

polyantibioticus mutant lacking a functional copy of this gene did not lose the ability to

synthesize DPO, thereby suggesting that a PA-CoA ligase is not involved in DPO biosynthesis.

However, due to the fact that six paralogous PA-CoA ligases (with an amino acid similarity of

24 %) were annotated in the S. polyantibioticus SPRT genome, it is plausible that one or more

of these enzymes may have suppressed the effect of the knockout of the paaK gene in S.

polyantibioticus strain ∆PAAK, which thereby resulted in a level of DPO production that was

comparable to the wild-type strain. Future work may necessitate the need to measure the exact

level of DPO production in both the S. polyantibioticus ∆PAAK and wild-type strains, as a

lower level of DPO production in S. polyantibioticus ∆PAAK could serve as circumstantial

evidence that a PA-CoA paralogue functions less efficiently than the dedicated enzyme in the

biosynthesis of DPO, thereby implicating the involvement of the enzyme encoded by

SPR_46390 in the production of DPO. Indeed, Geukens et al. (2006) demonstrated that Type

I signal peptidase (SPase) paralogous enzymes in S. lividans can only partly complement each

other, as clear differences in SPase substrate specificity resulted in a dramatic depletion of

preprotein processing and secretion.

The attempts made in this study to identify the genes responsible for the biosynthesis of benzoic

acid in S. polyantibioticus SPRT were based on characterised bacterial benzoic acid

biosynthetic pathways, as well as characterised bacterial amino acid degradation pathways.

Due to the fact that the in silico gene identification using a genome mining approach and


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subsequent in vivo gene disruption experiments disproved both hypotheses on how benzoic

acid is synthesized in S. polyantibioticus SPRT, the genes encoding this pathway are still

unidentified.

However, since the shikimate and chorismate pathways (Figure 5.4) are commonly used to

generate molecules with benzene rings in bacteria (and other organisms), S. polyantibioticus

SPRT could perhaps use a novel variation on one of these aromatic biosynthetic pathways to

generate benzoic acid. Indeed, intermediates from the shikimate pathway serve as starting

points for the biosynthesis of secondary metabolites in bacteria and plants (Herrman & Weaver,

1999; Herrman, 1995). Eukaryotic benzoate biosynthesis also proceeds via phenylalanine

derived from the shikimate pathway and, most importantly, a study by Hoffmann & Grond

(2004) postulated a direct conversion of shikimic acid to benzoate in Streptomyces griseoviridis

strain Tü 3634. In S. griseoviridis strain Tü 3634, the hypothetical mechanism of benzoate

formation consists of the dephosphorylation of shikimic acid-3-phosphate and subsequent

dehydration steps involving the enzymes 3-dehydroquinate dehydratase and shikimate

dehydrogenase. Shikimate is converted to benzoate in an alternative microbial route that has

not been described before and was confirmed by 13C feeding experiments. This proved that the

unsubstituted benzoyl ring in the final product originates directly from shikimate, contrary to

the plant-like conversion of shikimate to benzoate via prephenate, phenylalanine and

cinnamate, in which the carboxylic carbon of shikimate is lost in the latter stages (Figure 5.5)

(Hoffmann & Grond, 2004). However, the enzymes that convert shikimate to benzoic acid in

S. griseoviridis strain Tü 3634 have yet to be characterized.

It is possible that S. polyantibioticus SPRT employs a similar pathway for the biosynthesis of

benzoic acid directly from shikimate. As would be expected for a central metabolic pathway,

the enzymes involved in the shikimate pathway are all present in the S. polyantibioticus SPRT

draft genome, namely 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase

encoded by SPR_10690 and SPR_58840, 3-dehydroquinate synthase encoded by SPR_41260,

3-dehydroquinate dehydratase encoded by SPR_41270 and shikimate dehydrogenase encoded

by SPR_41230. A suggestion for future work would be to disrupt the genes encoding enzymes

in the shikimate pathway (Figure 5.4) in S. polyantibioticus SPRT, followed by assays to

determine whether DPO is still produced. If an S. polyantibioticus SPRT shikimate mutant was

unable to produce DPO, it would imply that the shikimate pathway is required to provide a


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precursor for DPO biosynthesis (i.e. benzoic acid). Once this had been established, further work

would be required to identify how benzoic acid is derived from shikimate (or one of its

precursors).

Another possible source of benzoic acid could be the mandelate metabolic pathway (Figure

5.6), which has been well characterized in Pseudomonas putida ATCC 12633 and allows

various pseudomonads to utilize mandelate as a sole carbon source via the oxidative

degradation of R-mandelate to benzoate (Tsou et al., 1990). Indeed the existence of

homologous enzymes from the P. putida ATCC 12633 mandelate catabolic pathway in the

draft S. polyantibioticus SPRT genome, including a mandelate racemase (encoded by

SPR_50530), a putative mandelate dehydrogenase (encoded by SPR_47860), a putative

benzoylformate decarboxylase (encoded by SPR_19760) and a putative benzaldehyde

dehydrogenase (encoded by SPR_9230) could confer on S. polyantibioticus SPRT the ability

to synthesize benzoic acid for DPO biosynthesis. However, due to the low degree of homology

shared between the S. polyantibioticus SPRT enzymes and the P. putida ATCC 12633 enzymes

involved in mandelate catabolism, and due to the fact that the genes for the enzymes identified

as putative mandelate pathway members in S. polyantibioticus SPRT are not clustered, it seems

unlikely that this method of benzoic acid synthesis is employed by S. polyantibioticus SPRT.

Another problem with any proposed mandelate-to-benzoate pathway is that an external source

of mandelate would be required and S. polyantibioticus SPRT is able to produce DPO in a

conventional bacterial growth medium from which mandelate is absent.


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Figure 5.4 An illustration of the shikimate pathway found in microorganisms and plants. In a sequence of

seven metabolic steps, phosphoenolpyruvate and erythrose 4-phosphate are converted to

chorismate, the precursor of the aromatic amino acids and many aromatic secondary

metabolites. All pathway intermediates can also be considered branch point compounds that

may serve as substrates for other metabolic pathways. The key enzymes involved in the

pathway are abbreviated in red: 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase

(DAHPS), 3-dehydroquinate synthase (DHQS), 3-dehydroquinate dehydratase (DHQD),

shikimate dehydrogenase (SD), shikimate kinase (SK), 5-enolpyruvylshikimate 3-phosphate

synthase (EPSPS) and chorismate synthase (CS). The direct conversion of shikimate to benzoic

acid, a branch point of the shikimate pathway, was postulated by Hoffman & Grond (2004) and

is catalysed by unknown enzymes.


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Figure 5.5 A depiction of the biosynthetic pathway leading to the synthesis of benzoic acid directly from

shikimic acid in S. griseoviridis Tü 3634 and ruling out the plant-like pathway via phenylalanine

described by Hertweck & Moore (2000), as established by 13C labelling experiments (Hoffman

& Grond, 2004).


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Figure 5.6 The P. putida ATCC 12633 mandelate metabolic pathway. Benzoate is subsequently converted

to acetyl-coA and succinyl-CoA by the enzymes of the β-ketoadipate pathway (Tsou et al., 1990).

Finally, benzoic acid biosynthesis in S. polyantibioticus SPRT may occur via the key

intermediate, chorismate. The chorismate pathway provides the aromatic building blocks for

secondary metabolites such as enterobactin, pyochelin and yersiniabactin (Van Lanen et al.,

2008). Chorismate can be converted to 4-hydroxybenzoic acid (4HBA) by the action of

chorismate lyase (Agarwal et al., 2014), of which three homologues (SPR_8160, SPR_40730

and SPR_74890) have been identified in the S. polyantibioticus SPRT draft genome.

Dehydroxylation of 4-hydroxybenzoic acid would lead to the formation of benzoic acid.

Indeed, the reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA has been


237

reported under anaerobic conditions in Pseudomonas species (Glöckler et al., 1989). However,

there are currently no reports in the literature suggesting that 4HBA can be aerobically

metabolized via dehydroxylation to benzoic acid (Fairley et al., 2002).

5.4 Proposed pathway for the biosynthesis of DPO in S. polyantibioticus

SPRT

Most NPRS gene clusters abide by the so-called colinearity rule whereby each module is

responsible for one discrete chain elongation step and the specific order of the modules defines

the sequence of the incorporated amino acids (Wenzel & Müller, 2005). However, contrary to

the hypothesis that a linear NRPS system with the standard C-A-PCP domain order would be

identified for DPO biosynthesis in S. polyantibioticus SPRT, the cluster exhibited a nonlinear

arrangement with the core domains arranged as A-PCP-C, in addition to stand-alone A, C and

PCP domains. Initially, these nonlinear NRPS systems were assumed to be exceptions to the

colinearity rule, however, numerous examples of nonlinear NRPS systems have been reported

in the past few years, and it has become increasingly apparent that they constitute a

considerable portion of the range of NRPSs found in nature (Mootz et al., 2002).

Based on the genome annotation analysis and gene disruption studies, a model for DPO

biosynthesis can now be proposed. The source of benzoic acid is yet unknown, as the pathway

for benzoic acid biosynthesis in S. polyantibioticus SPRT has not been established, despite the

efforts of this study to identify it. The acyl-CoA synthetase encoded by gene SPR_52860 is

proposed to select and activate benzoic acid as a CoA-thioester in the first step of the DPO

biosynthetic pathway (Figure 5.7).

As the substrate specificity of the A domain encoded by gene SPR_53060 is unclear (as it could

bind either phenylalanine or 3-hydroxyphenylalanine), an in trans phenylalanine hydroxylation

step is proposed. Indeed, FAD-dependent monooxygenases encoded by any of SPR_48520,

SPR_49640, SPR_52630 and SPR_53180 could provide the hydroxylase activity to catalyse

the β-hydroxylation of a phenylalanine residue in DPO biosynthesis. The A domain, encoded

by gene SPR_53060, is proposed to be responsible for the selection and activation of

3-hydroxyphenylalanine through ATP hydrolysis. The β-hydroxyphenylalanyl-adenylate

would then be transferred to the PCP domain, also encoded by SPR_53060, and formation of


238

the amide bond with benzoyl-CoA would be catalysed by the lone C/Cy domain encoded by

SPR_53040. Heterocyclization of the intermediate, benozyl-β-hydroxyphenylalanine to 4-

carboxy 2,5-diphenyloxazole would then be catalysed by the putative Cy domain encoded by

SPR_53060 operating in tandem with the C/Cy domain encoded by SPR_53040. Indeed, the

antiSMASH analysis, in addition to a multiple sequence alignment with the corresponding A-

PCP-C NRPS module from S. ambofaciens ATCC 23877T, revealed the existence of a large

putative “recognition sequence” at the C terminus of the C domain (SPR_53040) and at the N

terminus of the A domain encoded by SPR_53060. In contrast to standard COM domains

which normally facilitate the interaction between PCP and C domains located on separate

multienzymes (Hahn & Stachelhaus, 2006; Hahn & Stachelhaus, 2004), intersubunit protein-

protein interactions in the DPO biosynthetic pathway may establish interfaces between the A

(SPR_53060) and C/Cy (SPR_53040) domains to provide a functional pathway. Thus, the

recognition sequence would mean that the C/Cy domain encoded by SPR_53040 would

potentially interact with the A domain encoded by SPR_53060, thereby forming a conventional

C-A-PCP arrangement.

The oxidation of the hydrolytically labile oxazoline to form the oxazole moiety in the

heterocyclization reaction is proposed to be catalysed in a manner homologous to the oxidation

process observed in pyrimidine biosynthesis.

Decarboxylation would be carried out in trans by a putative decarboxylase, such as the enzyme

encoded by gene SPR_68606, which shares 30% amino acid homology to the decarboxylase

found in the tautomycetin biosynthetic cluster from Streptomyces griseochromogenes. This

reaction is required to convert 4-carboxy 2,5-diphenyloxazole to DPO.

The type II thioesterase, encoded by gene SPR_53090, would catalyse the release of DPO by

breaking the covalent linkage between DPO and the 4’-phosphopantetheine (4’-PP) thiol arm.

Even though the inactivation of the gene encoding this enzyme within the S. polyantibioticus

SPRT genome did not abolish DPO biosynthesis, the stand-alone type II TEs, often encoded

within NRPS gene clusters, do not play an essential role in NRP synthesis because their

removal from NRPS systems has been shown to decrease product titres, but not completely

eliminate peptide synthesis (Schneider & Marahiel, 1998).


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Finally, two NRPS domains found within the putative DPO biosynthetic cluster are believed

to be inactive. The PCP domain encoded by SPR_53070 is postulated to be inactive due to the

absence of the critical catalytic serine residue found in the conserved signature motifs of known

PCP domains (Chapter 3; Figure 3.7) and the C domain encoded by SPR_52900 is believed to

be inactive due to the absence of the H-H-x-x-x-D-G motif found in all active C domains.

Figure 5.7 Proposed DPO biosynthetic pathway in S. polyantibioticus SPRT.


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5.5 Conclusion and future work A gene cluster responsible for the biosynthesis of DPO was identified in this study and, based

on the genome annotation analysis and gene disruption experiments, a model for DPO

biosynthesis is proposed. At this stage, the model cannot account for the source of benzoic

acid, as in vivo gene disruption experiments disproved both of the hypotheses on how benzoic

acid is synthesized in S. polyantibioticus SPRT. However, alternative hypotheses regarding

benzoic acid biosynthesis in S. polyantibioticus SPRT have been put forward and are suggested

as the place to start in future studies to elucidate the production of this unusual starter unit in

DPO biosynthesis. The heterologous expression of the putative DPO gene cluster, identified

in this study, in host organisms such as ‘Streptomyces maritimus‘strain DSM 41777T, where

benzoic acid biosynthesis occurs, could be used as a method to confirm the involvement of

benzoic acid in DPO biosynthesis.

Future work should also involve the characterization of the substrate selectivity of the A

domains encoded by SPR_52860 and SPR_53060, in order to confirm their specificity towards

benzoic acid and 3-hydroxyphenylalanine, respectively, using an ATP-PPi exchange assay.

Additional liquid chromatography-mass spectrometry (LC-MS) analyses of the antibacterial

compounds produced by both the wild-type S. polyantibioticus strain SPRT and constructed

disruption mutants would confirm the identity of the bioactive compounds and further

corroborate the results obtained from HPLC and TLC-bioautography analyses, thereby

strengthening the preliminary hypothesis pertaining to DPO biosynthesis.

Additionally, DPO biosynthesis is most likely controlled by SPR_52890, the only gene in the

putative DPO biosynthetic cluster predicted to be involved in regulation. This gene encodes a

putative transcriptional regulator that contains a C-terminal DNA binding HTH domain and

belongs to the two-component response regulator family. In order to identify the gene cluster

responsible for the biosynthesis of benzoic acid in S. polyantibioticus SPRT, the presence of

cluster situated regulatory genes, such as SPR_52890, and/or promoter sequences can be used

as a tool to search for any interconnected pathways in the genome.

Moreover, this study was successful in the optimization of a transformation method for the

introduction of DNA into S. polyantibioticus SPRT. In light of this, future work should entail


241

gene disruption experiments in order to determine the involvement of the genes postulated to

be inactive, such as the PCP domain encoded by SPR_53070 and the C domain encoded by

SPR_52900. In addition, gene disruption of the genes identified in Chapter 3 as having an

unknown function in DPO biosynthesis will help to define the boundaries of the DPO gene

cluster.

Furthermore, the identification of the gene cluster responsible for DPO biosynthesis has laid

the foundation for combinatorial biosynthetic studies to create derivatives of DPO that might

be used in the treatment of drug-resistant tuberculosis. Lastly, the S. polyantibioticus SPRT

genome sequence could be explored further to identify the antibiotic gene clusters for other

potential antitubercular antibiotics that this organism produces.


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5.6 REFERENCE LIST

Agarwal, V., El Gamal, A.A., Yamanaka, K., Poth, D., Kersten, R.D., Schorn, M., Allen, E.E. & Moore, B.S. (2014). Biosynthesis of polybrominated aromatic organic compounds by marine bacteria. Nature Chemical Biology, 10: 640–647. Anterola, A. M., & Lewis, N. G. (2002). Trends in lignin modification: a comprehensive analysis of the effects of genetic manipulations/mutations on lignification and vascular integrity. Phytochemistry, 61(3): 221-294. Ashforth, E. J., Fu, C., Liu, X., Dai, H., Song, F., Guo, H. & Zhang, L. (2010). Bioprospecting for antituberculosis leads from microbial metabolites. Natural product reports, 27(11): 1709-1719. Baltz, R., H. (2008). Renaissance in antibacterial discovery from actinomycetes. Current Opinion in Pharmacology. 8: 557–563. Bérdy, J. (2005). Bioactive microbial metabolites. The Journal of antibiotics, 58(1): 1-26. Bernan, V. S., Greenstein, M. & Maiese, W. M. (1997). Marine microorganisms as a source of new natural products. Advances in applied microbiology, 43: 57-90. Bode, H. B., & Müller, R. (2003). Possibility of bacterial recruitment of plant genes associated with the biosynthesis of secondary metabolites. Plant physiology, 132(3): 1153-1161. Breese, K., Boll, M., Alt-Morbe, J., Schagger, H. & Fuchs, G. (1998). Genes coding for the benzoyl-CoA pathway of anaerobic aromatic metabolism in the bacterium Thauera aromatica. European Journal of Biochemistry, 256: 148–154. Fairley, D.J., Boyd, D.R., Sharma, N.D., Allen, C.C.R., Morgan, P. & Larkin, M.J. (2002). Aerobic Metabolism of 4-Hydroxybenzoic Acid in Archaea via an Unusual Pathway Involving an Intramolecular Migration (NIH Shift). Applied Environmental Microbiology, 68(12): 6246-6255. Garsin, D.A. (2010). Ethanolamine Utilization in Bacterial Pathogens: Roles and Regulation. Nature Reviews Microbiology, 8(4): 290–295. Geukens, N., Smitha Rao, V., Mellado, R.P., Frederix, F., Reekmans, G., De Keersmaeker, S., Vrancken, K., Bonroy, K., Van Mellaert, L., Lammertyn, E. & Anne, J. (2006). Surface plasmon resonance-based interaction studies reveal competition of Streptomyces lividans type I signal peptidases for binding preproteins. Microbiology, 152: 1441-1450. Glöckler, R., Tschech, A. & Fuchs, G. (1989). Reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA in a denitrifying Pseudomonasspecies. FEBS Letters, 251: 237-240. Gulick, A.M. (2009). Conformational Dynamics in the Acyl-CoA Synthetases, Adenylation Domains of Non-Ribosomal Peptide Synthetases, and Firefly Luciferase. ACS Chemical Biology, 4(10): 811-827. Hahn, M. & Stachelhaus, T. (2006). Harnessing the potential of communication-mediating domains for the biocombinatorial synthesis of nonribosomal peptides. Proceedings of the National Academy of Sciences USA, 103: 275-280.

http://aem.asm.org/search?author1=D.+J.+Fairley&sortspec=date&submit=Submit


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Hahn, M. & Stachelhaus, T. (2004). Selective interaction between nonribosomal peptide synthetases is facilitated by short communication-mediating domains. Proceedings of the National Academy of Sciencse USA, 101: 15585-15590. Harvey, A.L. (1999). Medicines from nature: are natural products still relevant to drug discovery? TiPS, 20: 196-198. Herrman, K.M. (1995). The Shikimate Pathway as an Entry to Aromatic Secondary Metabolism. Plant Physiology, 107: 7-1 2 Herrman, K.M. & Weaver, L.M. (1999). The Shikimate Pathway. Annual Review of Plant Physiology and Plant Molecular Biology, 50: 473–503. Hertweck, C. & Moore, B.S. (2000). A plant-like biosynthesis of benzoyl-CoA in the marine bacterium 'Streptomyces maritimus'. Tetrahedron, 56: 9115-9120. Hill, A.M., Thompson, L.B., Harris, J.P. & Segret, R. (2003). Investigation of the early stages in soraphen A biosynthesis. Chemical Communications, 12: 1358-1359. Hoffmann, L., & Grond, S. (2004). Mixed Acetate‐Glycerol Biosynthesis and Formation of Benzoate Directly from Shikimate in Streptomyces sp. European Journal of Organic Chemistry, 2004(23): 4771-4777. Hojati, Z., Milne, C., Harvey, B., Gordon, L., Borg, M., Flett, F. & Micklefield, J. (2002). Structure, biosynthetic origin, and engineered biosynthesis of calcium-dependent antibiotics from Streptomyces coelicolor. Chemistry & biology, 9(11): 1175-1187. Jansen, R., Kunze, B., Reichenbach, H., Jurkiewicz, E., Hunsmann, G. & Höfle, G. (1992). Antibiotics from Gliding Bacteria, XLVII. Thiangazole: A Novel Inhibitor of HIV-1 from Polyangium spec. European Journal of Organic Chemistry, 4: 357-359. Juguet, M., Lautru, S., Francou, F. X., Nezbedová, Š., Leblond, P., Gondry, M. & Pernodet, J. L. (2009). An iterative nonribosomal peptide synthetase assembles the pyrrole-amide antibiotic congocidine in Streptomyces ambofaciens. Chemistry & biology, 16(4): 421-431. Kaneko, M., Ohnishi, Y. & Horinouchi, S. (2003). Cinnamate:Coenzyme A Ligase from the Filamentous Bacterium Streptomyces coelicolor A3(2). Journal of Bacteriology, 185(1): 20–27. Keating, T. A., Miller, D. A., & Walsh, C. T. (2000). Expression, purification, and characterization of HMWP2, a 229 kDa, six domain protein subunit of yersiniabactin synthetase. Biochemistry, 39: 4729-4739. Kelly, R. A., Scott, N. M., Díez-González, S., Stevens, E. D. & Nolan, S. P. (2005). Simple synthesis of CpNi (NHC) Cl complexes (Cp= cyclopentadienyl; NHC= N-heterocyclic carbene). Organometallics, 24(14): 3442-3447. Koetsier, M., Jekel, P., van den Berg, M., Bovenberg, R. & Janssen, D. (2009). Characterization of a phenylacetate-CoA ligase from Penicillium chrysogenum. Biochemical Journal, 417: 467-476. Koetsier, M.J., Jekel, P.A., Wijma, H.J., Bovenberg, R.A.L. & Janssen, D.B. (2011). Aminoacyl-coenzyme A synthesis catalysed by a CoA ligase from Penicillium chrysogenum. FEBS letters, 585(6): 893-898.

http://www.jbiomedsci.com/sfx_links?ui=1423-0127-19-89&bibl=B33


244

Kunigami, T., Shin-Ya, K., Furihata, K., Hayakawa, Y. & Seto, H. (1998). A novel neuronal cell protecting substance, aestivophoenin C, produced by Streptomyces purpeofuscus. Journal of Antibiotics (Tokyo), 51(9): 880-882. Kyndt, J.A., Meyer, T.E., Cusanovich, M.A. & Van Beeumen, J.J. (2002). Characterization of a bacterial tyrosine ammonia lyase, a biosynthetic enzyme for the photoactive yellow protein. FEBS Letters, 512: 240–244. Le Roes, M. (2005). Selective isolation characterization and screening of actinomycetes for novel anti-tubercular antibiotics. PhD Thesis, Department of Molecular and Cell Biology, University of Cape Town. Chapter 5: 167-182. Le Roes-Hill, M. & Meyers, P. R. (2009). Streptomyces polyantibioticus sp. nov., isolated from the banks of a river. International Journal of Systematic and Evolutionary Microbiology, 59: 1302–1309. Li, X., Zvanych, R., Vanner, S. A., Wang, W., & Magarvey, N. A. (2013). Chemical variation from the neoantimycin depsipeptide assembly line. Bioorganic & medicinal chemistry letters, 23(18): 5123-5127. Li, B. & Walsh, C.T. (2010). Identification of the gene cluster for the dithiolopyrrolone antibiotic holomycin in Streptomyces clavuligerus. Proceedings of the National Academy of Sciences, 107(46): 19731-19735. Ligon, J., Ligon, J., Hill, S., Beck, J., Zirkle, R., Molnár, I., Zawodny, J., Money, S. & Schupp, T. (2002). Characterization of the biosynthetic gene cluster for the antifungal polyketide soraphen A from Sorangium cellulosum So ce26. Gene, 285: 257-67. Linne, U. & Marahiel, M. A. (2004). Reactions catalyzed by mature and recombinant nonribosomal peptide synthetases. Methods in enzymology, 388: 293-315. Lombó, F., Velasco, A., Castro, A., De la Calle, F., Braña, A. F., Sánchez‐Puelles, J. M. & Salas, J. A. (2006). Deciphering the biosynthesis pathway of the antitumor thiocoraline from a marine actinomycete and its expression in two Streptomyces species. ChemBioChem, 7(2): 366-376. Michal, G. (1999). Biochemical Pathways. Spektrum Akademie Volume 1. Verlag, Heidelberg. Marshall, C. G., Hillson, N. J., & Walsh, C. T. (2002). Catalytic mapping of the vibriobactin biosynthetic enzyme VibF, Biochemistry, 41: 244-250. McQuade, T. J., Shallop, A. D., Sheoran, A., DelProposto, J. E., Tsodikov, O. V. & Garneau-Tsodikova, S. (2009). A nonradioactive high-throughput assay for screening and characterization of adenylation domains for nonribosomal peptide combinatorial biosynthesis. Analytical biochemistry, 386(2): 244-250. Mootz, H.D., Schwarzer, D. & Marahiel, M.A. (2002). Ways of assembling complex natural products on modular nonribosomal peptide synthetases. ChemBioChem, 3: 490-504. Navarro-Llorens, J.M., Patrauchan, M.A., Stewart, G.R., Davies, J.E., Eltis, L.D. & Mohn, W.W. (2005). Phenylacetate Catabolism in Rhodococcus sp. Strain RHA1: a Central Pathway for Degradation of Aromatic Compounds. Journal of Bacteriology, 187(13): 4497-4504. Nerud, F., Sedmera, P., Zouchov´a, Z., Mus´ılek, V. & Vondr´aˇcek, M. (1982). Biosynthesis of mucidin, an antifungal antibiotic from basidiomycete Oudemansiella mucida 2 H-, 13 C-, and 14 C-labelling study. Collection of Czechoslovak Chemical Communications, 47: 1020–1025.


245

Phelan, V. V., Du, Y., McLean, J. A., & Bachmann, B. O. (2009). Adenylation enzyme characterization using γ-18 O 4-ATP pyrophosphate exchange. Chemistry & biology, 16(5): 473-478. Rausch, C., Weber, T., Kohlbacher, O., Wohlleben, W. & Huson, D. H. (2005). Specificity prediction of adenylation domains in nonribosomal peptide synthetases (NRPS) using transductive support vector machines (TSVMs). Nucleic acids research, 33(18): 5799-5808. Rhee, S. K. & Fuchs, G. (1999). Phenylacetyl‐CoA: acceptor oxidoreductase, a membrane‐bound molybdenum–iron–sulfur enzyme involved in anaerobic metabolism of phenylalanine in the denitrifying bacterium Thauera aromatica. European Journal of Biochemistry, 262(2): 507-515. Rohr, J. (1997). Biosynthesis of Taxol. Angewandte Chemie International Edition, 36: 2190-2195. Rother, R., Poppe, L., Viergutz, S., Langer, B. & Retey, J. (2001). Characterization of the active site of histidine ammonia-lyase from Pseudomonas putida. European Journal of Biochemistry, 268: 6011–6019. Roy, R., Gehring, A., Milne, J., Belshaw, P. & Walsh, C. (1999). Thiazole and oxazole peptides: biosynthesis and molecular machinery. Natural product reports, 16(2): 249-263. Schaffer, M.L. & Otten, L.G. (2009). Substrate flexibility of the adenylation reaction in the Tyrocidine non-ribosomal peptide synthetase. Journal of Molecular Catalysis B: Enzymatic, 59: 140-144. Schneider, S., Mohamed, M.E. & Fuchs, G. (1997). Anaerobic metabolism of l-phenylalanine via benzoyl-CoA in the denitrifying bacterium Thauera aromatica. Archives of Microbiology, 168: 310–320. Schneider, A. & Marahiel, M. A. (1998). Genetic evidence for a role of thioesterase domains, integrated in or associated with peptide synthetases, in non-ribosomal peptide biosynthesis in Bacillus subtilis. Archives of microbiology, 169(5): 404-410. Schupp, T., Toupet, C., Cluzel, B., Neff, S., Hill, S., Beck, J.J. & Ligon, J.M. (1995). A Sorangium cellulosum (myxobacterium) gene cluster for the biosynthesis of the macrolide antibiotic soraphen A: cloning, characterization, and homology to polyketide synthase genes from actinomycetes. Journal of Bacteriology, 177: 3673-3679. Schuster, B. & Retey, J. (1995) The mechanism of action of phenylalanine ammonia-lyase: the role of prosthetic dehydroalanine. Proceedings of the National Academy of Sciences USA, 92: 8433–8437. Schwarzer, D., Finking, R. & Marahiel, M.A. (2003). Nonribosomal peptides: from genes to products. Natural Product Reports, 20: 275-287. Schwede, T.F., Retey, J. & Schulz, G.E. (1999). Crystal structure of histidine ammonia-lyase revealing a novel polypeptide modification as the catalytic electrophile. Biochemistry, 38: 5355–5361. Seipke, R.F. & Hutchings, M.I. (2013). The regulation and biosynthesis of antimycins Beilstein Journal of Organic Chemistry, 9: 2556–2563. Steller, S., Vollenbroich, D., Leenders, F., Stein, T., Conrad, B., Hofemeister, J. & Vater, J. (1999). Structural and functional organization of the fengycin synthetase multienzyme system from Bacillus subtilis b213 and A1/3.Chemistry & biology, 6(1): 31-41.

http://www.ncbi.nlm.nih.gov/pubmed/?term=Seipke%20RF%5Bauth%5D

http://www.ncbi.nlm.nih.gov/pubmed/?term=Hutchings%20MI%5Bauth%5D


246

Tang, L., Zhang, Y. & Hutchinson, C.R. (1994). Amino Acid Catabolism and Antibiotic Synthesis: Valine Is a Source of Precursors for Macrolide Biosynthesis in Streptomyces ambofaciens and Streptomyces fradiae. Journal of Bacteriology. 176(19): 6107-6119. Tsou, A.Y., Ransom, A.C. Gerlt, J.A., Buechter, D.D., Babbitt, P.C. & Kenyon, G.L. (1990). Mandelate Pathway of Pseudomonas putida: Sequence Relationships Involving Mandelate Racemase, (S)-Mandelate Dehydrogenase, and Benzoylformate Decarboxylase and Expression of Benzoylformate Decarboxylase in Escherichia coli. Biochemistry, 29: 9856-9862. Van Lanen, S. G., Lin, S., & Shen, B. (2008). Biosynthesis of the enediyne antitumor antibiotic C-1027 involves a new branching point in chorismate metabolism. Proceedings of the National Academy of Sciences, 105(2): 494-499. Wenzel, S.C. & Müller, R. (2005). Formation of novel secondary metabolites by bacterial multimodular assembly lines: deviations from text book biosynthetic logic. Current Opinions in Chemical Biology, 9:447-458. Wright, G. D. (2012). Back to the future: a new ‘old’lead for tuberculosis. EMBO molecular medicine, 4(10): 1029-1031. Wu, D., Hugenholtz, P., Mavromatis, K., Pukall, R., Dalin, E., Ivanova, N. N. & Eisen, J. A. (2009). A phylogeny-driven genomic encyclopaedia of Bacteria and Archaea. Nature, 462(7276): 1056-1060. Zhang, W., Ostash, B. & Walsh, C. T. (2010). Identification of the biosynthetic gene cluster for the pacidamycin group of peptidyl nucleoside antibiotics. Proceedings of the National Academy of Sciences, 107(39): 16828-16833.

Appendix A

247

APPENDIX A

Figure A1. Genome map of the draft S. polyantibioticus SPRT genome generated using the CLC Genomics

Workbench 7.0.4 (CLCbio, Denmark). Arrows represent the relative positions of the secondary metabolite clusters discussed in Chapter 3, where (A) is the NRPS gene cluster spanning the region located from nucleotide 637827-688770, (B) is the NRPS gene cluster spanning the region located from nucleotide 669778-735243, (C) is the NRPS gene cluster spanning the region located from nucleotide 3093585-3154158, (D) is the NRPS gene cluster spanning the region located from nucleotide 3320540-3386004, (E) is the NRPS gene cluster spanning the region located from nucleotide 5343994-5398013 and (F) is the NRPS gene cluster spanning the region located from nucleotide 5634984-566500.

Appendix B

248

APPENDIX B

Nucleotide sequences of the genes preliminarily identified as components of the DPO

biosynthetic gene cluster are provided in this appendix.

> SPR_52860

ATGCCCTCGACCACTGAATCCGCCGCCACGCTGTGGGAGCTCATCGACCGGGCCGTACGCCTCTCCCCCGCGGCC

ACCGCCGTACGCCAGGGAACGCGGGCCCTCACCTTCCGCGAACTCGCCGACCGCGTCGAGACCACAGCACGCCGC

CTGCGCACGCGCCTGCCCGCCGACGGCGGAGGAACCGTGGGCCTGCTCTTCGAGAACACCGTGGAGAGCACGGTG

GCCTTCCTGGGCGCGCTGTACGCGGGCGTACCCCTCACGCCCCTCGAACCCGACAGCACCGAGCCCCATCTCCTG

GGCGTGCACCGGGACTTGGGACCCCTGCACCTCGTCGGTCGGCAGGCGAGGCTCAGCACACTGGCCCCTCCCGCT

GCCACCTCACTCGCCGCCCGGTGGCAGGGCGGTGTCCTCATCGACGTGGACGAGCTCACCGCCCGCCCCGGCGCG

GCGGCCCCGTCGGCGCCGCTGCCCGCGCCGCCGCCCGACGCCCCCGCGCTCTACCAGTACACCTCCGGCTCGACC

GGCGAGCCGAGGGCCGCCGTGCACTCACAACACGACCTGGTCCGCGGTGGCGAGATCTACGCCCGCACCTACGGC

ATCACCCCGGCCGACCGGATTCTCGCGGCCGTACCCCTGCTGCACTCCTTCGGCATGGTCGCCGCGCTCGCCACC

GCGCTGCACGCCCGCGCGGAGCTCGTCCTGCTCGGCCGGTTCGCACCGGCCGAAATGCTCCGGGCACTGCACCAG

CACGCCTGCACCATCGTGGTGGGCACCCCGCTCGCCTATGACCTGGCGGCCCGTTCGGCGGCCTCGCGCAGCGAG

ACGTCCCGCCCGGGCGACACCGTACGGCTCTGTCTGTCCTCCGGGGCGGCCCTGCCCCCGGCCGTGGCGGACCGC

TTCGCCCAGCACTGCGGCCCGGCCGTCCAGCAGGTCTACGGAAGCACCGAGGCCGGTGTCGTCGCCGCGCAGCTC

CCGCAGCCGGACGGCACGGCCGATGCCGGGGTGGGCAGGCCGGTGCCCGGGGTACGGATCCGCCTGGTGGACGAG

GAGGACCGACCGGTTCCGCCGGGCGGCACGGGCGCCCTGCTCGTGCGCACCCCCGCCATGTTCACCCACTACCTC

GGCCACCCGGGCCCGTCCGAACGAGCCTTCCGCGACGGCTGGTACGTCACCGGCGACCTGGCGCGCCTCGACGGT

GACGGCCGTCTGCACCTGGTGGGCCGCAAGGAGTCCTTCATCAACGTCGGTGGCAAGAAGGTCAATCCCCTGGAG

GTCGAAGCGGCCCTGCTGGCCCACCCGGCCGTCGCCGAGGCCGTGGTCTGGGGCGAGGTCGTGGAGGAACAGACC

AGCGAGCGCGTACGGGCAGCCGTGGTGCCGTGCTCCCCGCTCAGCGGGGCCGCGATCACCGCGCACTGCCGTGAC

CGGCTCCTGGCCCATCAGGTGCCCGCGACGATCGAGTTCGTGGCGTCGCTGCCCAAGACCTCCCTGGGCAAGATC

CGCCGCGCGGCCGTGGCCGGAGCCGCCCCCGCACGGCACCGGGACGACACGGCCTGA

> SPR_52870

ATGGCACTTCTGGACGGCATCGAGGCGGGCGCCGAGGACGCCTACGACCGCCATTACGGCGACCGGCAGCTGCTG

CGCCGCATCACCCCCTACTTCCAGGGCCGCGGCGGCGCGGTGGCCTTCGTCACCGCGGCGGTGGTCGTGGCGGCG

GCCGCGGGCAGCGCCGTACCGATCCTGCTGGCCCGCACCGTCGACTCGGCCCTGGACGACGACACCCGGTCGGCG

ATGACACTGCTAGCCGTTGCCGTCCTCCTCACCGGCGCCGCGGCCTGGCTGTTCACCGTCCTCCAGCAGCGCCTC

ACCGGCACCCTTGTCGGCGACGCGGTGCTGCAACTGCGCGAACACGCCTTCGCCGCGGCCGTACGCCAGGACCTC

GCGTTCTACGACACCCACCCCACGGGCCTGGTGGTCAGCCGCGTCACCAACGACACCCAGACGTTCGGTGCCCTG

CTCTCCCTGGTGCTCTCCCTCATCGGTCAGGTCCTCGTCGTCCTGCTGATCCTGACGGCACTCTTCGTCATCAAC

GTGCCGCTGGCGCTGCTCACCACCGTGGTGGTCGCCCTGATCGTCGCGGTCAGCCTCGCCTTCAGGAAACGCGCG

CGCACCGCCTCCACCCGCCAGCAGCAGGCCCTCGCCGAGGTCAGCGGCTATGTGCAGGAGACCCTGCGCGGGATC

ACGGTGGCCCGCAACCACCGCGGCGAATCGGCGGCCGAAGCGGGGCTGCGGGCGGTCAACGGCCGCTGGTACCAG

GCCAGTGTGCGCCTCAACCGCCTCTTCAGCGGCATCTTCCCGCTGCTCATCTCCCTGACCGGACTGGGCACGACG

GCGGTGGTGCTGGCCGGCGGCCACCAGGTCGCATCCGGCGACATCTCGGCCGGCGAATGGGTCCTCTTCCTGGAG

GCCCTGGCCCTCTTCTGGTCGCCGGTCGCCACCATCGCCTCCTTCTGGCAGCAGCTCCAGCAGGGCCTCTCGGCC

GGGGAGCGGATCTTCGCGCTGATCGACCGGGAACCCGCCGTCCACCAGAGCGCCCAGCTGCCCCCGCCCCGTCTG

CGCGGCGCACTCGAACTGCGCGGCGTCAGCTTCCGCTACACCCCCGAGCGGCCCGTCCTCCACGACATCGACCTC

ACCGTCGCGGCCGGGGAGACCGTCGCACTGGTCGGCCACACAGGGGCGGGCAAGTCCAGCCTGGTGCGCCTGCTG

ACCCGCTCGTACGAGTTCCAGGAAGGCAGCCTGCTCGCCGACGGCCGGGACGTGCGGACCTTCGACCTGGCGCAG

TACCGGCGCTGCCTCGGCGTGGTCACCCAGACGCCCTACCTCTTCTCCGGCACCGTCGCCGAGAACATCGCGCTG

GGCCGGCCGGGCGCCGACCGCGCGGCCATCGAGGCCGCGGCCCACGCGGTCGCCTCCGGCGCCTGGCTGCGGCAG

Appendix B

249

CTGCCCGACGGCCTCGACACACCGACCGACGAAGGCGGCCGCAACCTGTCGACCGGGCAGCGGCAGATCGTGGCG

CTGGCCCGGGTGTTCCTGCAGGACGCCCCGATCTTCATCCTCGACGAGGCCACCGCCAGCGTCGACCCGCTCACC

GAGGCCCAGATCCAGGAAGGACTCGACGCGCTCGCGGCGGGGCGCACCACCATCGTCGTGGCGCACCGGCTCCCC

ACCGTCCGCAAGGCCGACCGCATCGTCGTCGTCGACGACGGGCGCCTCGTCGAACAGGGCGACCACGCCACCCTG

ATGCGGCAAGGCGGTGCCTACAGCCGCCTCTACCGGCAGTACTTCCACCATCAGCACCCCGACCACGACCCCGCC

GACGACCCGTCCGGCACCGGGCGGGCGCCGGTCGGCGCGGGGCCGCACCTAGCGGAGGCCAGCGATGCCCTCGAC

CACTGA

> SPR_52880

ATGACGACCGAGACCGCCGCGCAGACCCGCTCCGCGTCCGGACCGGCGCCGGCCACCGGGCCCGAACTGACCATC

GGCCACTGGCTCCGCCTGCACATGCGTCACTTCCGCCGGCACATCGCGGTCCATCTGACCGGAAGCCTGCTCTGG

CAGTCCCTCACCGCGGCCCTCCCCCTGGTCATCGGGCTGGCCTTCGACGCCGTACTGAAGACCAACGGGCGGGAA

CCTGATCTGGGGGCCCTGCACGCCGTGTGCGCGGCACTGCTCGCCCTGGTCCTCGTCCGGGGCGTCTGCGGCATC

GCCTCCACCTACGCCCTGGAGGCCTTCGCCAGCGGCCTTGAACGCGACGCGCGGGCCGGCGTGTTCGCCAGCATG

CTCCGCAAGAAGCAGGGCTTCTTCAACCGGCACCGCACCGGCGACCTGTCCACCCGCGCCACCGGCGACGCCGAG

GCACTCGGACTCATGGTGTCGCCGGGCTTCGACATGACCCTCGACATGGCGCTCAACACCCTCATTCCGCTGGTG

TTCATCGCGGCCGTCGACTGGCGGCTCCTGCTCTTCCCCGGGATCTTCGTCGTCCTGTTCGTCGCCGCCCTCATG

GATCACGGGCGGCGCCTCGAACCGGTCTCCGACCTCACCCGCGAGGAGTTCGGCGCGATGTCCGCCCAGGCCGCC

GAGAGCATCACCGGAATCGAGGCGGTCGAGGCGACCGACGGAGCGGAGCGCGAGCAGGACCGCTTCCGCCGCACC

GCCACCGCCTACCGGGACGCCGCCGTGGCGCAGGCACGCGTCCAAGCCCTGTCCTTCCCCCCGCTGCTGCTCGCC

GTGGCCACCGCCGGAACGCTGCTCCACGCCGTCTTCCTGCTGCGCGACGGCTCACTGAGCGTCGGTGAACTCGTC

GCCGTCCTGGGCCTGATGAGCACGCTGCGCGCCCCCACCCAGCTCGCCTCCTTCAGCATCGGGCTCATCTTCTTC

GGACTCTCCGGCGCACAGCGCATCCTGGAGATCATCAACGACCGGGCGGGAGAGGACGAGGAGGGAGGCCGGCAC

GAGGCGGTCATCACCGGCGAAGTGGTCTTCGAGAACGTCACCTTCGCCTACGGAAACGGCAAGCCCGTGCTGCGC

GACATCTCCTTCCGCGCCGCCCCCGGCACCACCGTCGCCGTCGTCGGCGCCACCGGCAGCGGCAAGTCCACCCTG

CTGCACCTGCTGAACCGCACCTACGTGCCCACCGAGGGCCGCGTCCTCGTCGACGACGTGGCCACCACCGCCTGG

GACCCCTCGGCACTGCGCGGCCAAGTAGCCGTCGTCGAGCAGGACGTGGTCCTGTTCTCCCGCACCATCGCCGAG

AACCTCGCCTTCGGCGCCGCACCGGACACCGGCCGGGCCCAACTGGAAGAGGCGGCCCGTACCGCCCAGGCGCAC

GACTTCGTCATGGCGAGCGAGCACGGCTACGACACCGTGCTGGGCGAGCGCGGCGTCACCCTCTCCGGCGGCCAG

CGCCAACGCCTCGCCATCGCCCGGGCGTTGGTGACCGACCCGCGCATCCTCGCCGTGGACGACGCGACCAGCGCC

GTCGACAGCGTGACCGAACACGAACTGCAGCTCGCCATGCGGCGCGCCGCCACGGGCCGTACCACCTTCCTCGTC

ACCCCCCGGCTGTCCCGCATCCGCGCCGCCGACCACATCGTCGTCCTCGACGCGGGCCGGGTCGTCGGCCAGGGC

ACCCACGAACACCTCCTGCGCACCTGCGCGTTCTACCGCACGATCTTCGCGCCGTACGCACTGCCGGCCGCGGAG

GGAACCACCACCGCCGCCGTCGCGGCCGGGGCAGAGGAAGGAACCCGCTGA

> SPR_52890

GTGAGCGATTTAGCATGCAAACCCCCCGCCCCGTCGCGACCGCTGGTCGTCGCGACTCTTGTCCACGACGGCCTC

GCGCGCCAGGAGCTGCAGACCGCTCTGGCACAGGCCGCCCTCGTGCGCGAAGCCCGGCACTGCGCCGACCGACGC

GAGGCGCGGGAGGCTCTGGACTCCGGCCGGGTCGACGTGTTCGTCGTGGCCAGGAGCGACTACGACGCCCATGCC

GACTTGCTTGACGACTTCCGCTCGCCCCTGCCGAGGATGCTTGTGCTGTTGAGTCATGCCGATCCGGACGAAGCG

ATGCTGTCCGGGCCACCAGCGCCCGATGGATTCCTGCTGCAGGGCGGTCTGAGCGCCGCCGATGTGGACAGCGCG

CTGCGGCGCATGGCCGCGGGCGAGGTACCGATGCCGGCCCTGCTCGCCCGCGCCCTGATGGACCGTGCCAGCACG

AGCCGCCTGCCGCACGGCCGACATGACATCGCTGTCACCGCCCGGGAGACCGAGGCGCTGCTCCTGCTCGCCGAG

GGGCTGAGCAACAAGCAGATGGCCCGGCGGCTGGAGATCACCAGCCATGGCGTGAAACGGCTCGTGGCCAGTCTG

CTGCTCAAGCTCGGGGCGCCGAACCGGACGGCTGCCGTGGTCCTGGCCATCCACGCGGGTCTGATCCGCACGACC

CGGCCGGGCCAGGGCACGGCGGACCGCCGGGTGGTACGGGTCCAGCTCGCGGGGGGTGGAGCGGACGTCCGCCTC

CCGGTCCCCGCCGTGCGCTTCCTCGGTGAGGAGGTGCCCGAGGAGCGCGCCTCCTGA

> SPR_52900

GTGGAAAAAATCGAGACGCGTGATGTCCCCTTCTACGGTCGCCGTTCGGTCATGGCGTCGGCCACCTGTGCACAG

CGGCAGATGTGGGACCTGATCCGACGGGAAATTCCCGACGGCTCCTTCTACGATTTCTGCCACGAGGTTTCCCTT

ACCGGCGAAGGAACCGTGGATGACGTTCTCGCCGTATGCGCGGAACTCCTCTCCCGGCATGAGTCGCTGCGTACG

GCATTTTTCTGCGGTGCGGACGGGAAATTGGTGCAGAGCGTGGCGCGGTCCGGATCCTTCGAGGCGGAGATATGC

GCCACCGGGCCCGGCGAGAGCGCGCAATTCGTGTACGACGCCTGGCGGCGGCGGATGCGGGACAGGACGTTCGAC

CTGCGGAACGGCCCGCCGCTGCGGGCGCTGGTCGTCGTCACCGGGCACGCGCCCGTCATGGCGGCCTTCTGTGTC

TCGCACCTGGCCGCGGACCTCATGTCGATGCGCACGCTGGCCGGTGAAGTCCTGCCCCTGCTGGCCGCGCGGATC

GCCCGTASCCCCGCCCCGCCGCCCGCCGTGACGCGCCAGCCGGTCGAACAGGCCGACTTCGAGCACTCCCCACAG

GGGCGCGCCCTGCTGGCCCGGGCCCACACACACTGGCGGCAGCAGCTGGCGAGCGCCCCCACCACGATGTTCCCC

Appendix B

250

GGCCGTCCCGCCCCGCAGGGGCCCGGCCGACCGGACCGCTACAGCGCGGCCATGGACTCCGCGGCCGCCTTCCTT

GCCATCCGTGCCCTGGCCGTCCGGTGGCGGGTGAGCACCTCCGCGGTGCTCCTCACAGCGGTCGCACTGCTGCTC

GGCGCCCGCTCCGGGCAACAGACCTGCGCCCTGAGGCTGTTGGCCGCCAACCGCACGCACCCCGCACTCCAGCGA

AGCGTGGCCAACCTGCACCAGGAGGTCCTCACCAGCTTCGACCTGCGCGGGGAGAACGTGCGGGCCGTCGCCCGC

CGCGCCTTCGCCGCGGGGACCCTCGCGTACGCCAACGGCCTGTTCGACCCCGACGGGGCGAACGAGCTGATCCGG

GCCGAAGGGCGCAGGAGGGGCGAGCCGCTCCAACTGTCCTGCTGCTTCAACGACATCCGCACCGACCACGATCCG

CGGAGTCCGGGCGGGACGGCGTCCGCCGAGCAGATCCGCGCCGCCCTGGCCCGTACCGTCGTCGCCTCCAGCGAC

TTCGAGGAAGCGGAGACCTTCTTCCTGGTCGTCGTCGACACCGACCCCGGGTGGCTCAGGTTCGTGCTGTGCGCC

GAGACGGCCGCCCTGTCGCCCGAGGAGGTGCACATCTTCCTCCGCGACCTCGAACGGCTCCTCGTGGACTGCGCC

GAGCAGCCCGAACGTTCCTGGCCACGACTCGATCAGGGCCGGGGCCCGCAGGCCGCCCAGCCACCGCGGACGGCT

GCCCGGGGATGA

> SPR_52910

ATGCCGCAGCACCGGGTGACGGGGGAGTCGACTGTGTTCACGGAAGCATTGGCACGTGAGGCTGCCATGGACGTG

GAGAACCCCGCGCACGGCACGGTGTTCGCGCAGGCTCCCCGCTGCACCGCCGCCGAACTCGACGCGGTCCTCGCC

GCCTCGGCCCGGGCGTTCCCCGGGTGGGCGGCACTGCCGCTGGAGAGCCGGCGTCCGTACCTGCTCGCCTGCCGG

GACGCGCTGCGCGACGCCGAGGACGACGTCGCGGACCTGCTGACCCGGGAACAGGGCAAGCCGCTGCGGCACGCG

CACCACGAAGTGCGGCTGGCCGCCGACTGGTTCGCGCACACCGCCGAACTCGCCCTGCACGCCGACCGGATCGTG

GACGAGCCGACGGCCCGCGTCACCCTGGAGCGGGTGCCGCACGGTGTCGTCGCGGCGATCGCCCCCTCCAACTAC

CCCGTCCTGCTGGCCGTGTGCAAGATCGCCCCGGCGCTCCTGGCGGGCAACACGGTCGTCCTCAAGCCCTCGCCC

GCCACCCCGCTGTCCAGCCTGCTCATGGGCGAGGTGCTGGGACGGGTCCTGCCGCCCGACGTCCTGCGGGTGATC

AGCGGCGACGCCGCGCTGGGGGCCCGGCTCACCGCACACCCGGCAGTGCGGCTGATCTCCTTCACCGGCTCGATC

GCCGCCGGCCGCGCCATCGCCCGGTCCGCCGCCGCGGACTTCAAACGGACCGTCCTGGAGCTGGGCGGCAACGAC

CCGGCCATCGTGCTGCCCGGCGCCGACGCACAGGCCCTGGCGCGTCCGCTGTTCGACCGGGCGATGGTCAACAGC

GGCCAGTTCTGCGCCGCGGTCAAGCGCGTCTACGTGCCGCGAGCCCAGCACGCCAAGCTCACCGCGGCCCTGGCC

GCGCCGGCCGAGGCCACCGTGGTCGGTGACGGCCTCGACGCCGCGACCGAACTCGGCCCGCTGGTCAGCCGTGAG

CAGCTCGCCCATGTGACCGCGCTGGTGGGCGACGCGGTGCGGCGGGGCGCCCGGCTCGTCACCGGGGGCCGCGCC

CTGGAGCGGCCCGGCCACTTCTATCCCCCCACCGTCGTCACGGACTTGCCGCAGGGGACGCGGCTTGAGGAGGAG

GAACAGTTCGGCCCCGTGATCCCCGTGATCGCGTACGACGATCTCGACGCCGTGACGGCCCGCGTCAACGCGTCC

CCCTACGGGCTGGGTTGCTCCCTGTGGGGCGATCCGGAACAGGCCGCCGCGGCGGCCCGGCGGCTGGACTGCGGA

ACGGTGTGGATCAACACCCACGGCGACCTCAGACACGACGTGCCGTTCGGCGGCCACCGGCACTCGGGCACGGGC

GTCGAGTACGGAGCGTGGGGCCTCCTGGAATACACCCAGATCACCATCCACCACCTCGCGCTGCGCGGGGGAGAT

GAGGGGAAGGCATGA

> SPR_52920

ATGAGCGAAACCACCTCCGGCGGCGCCCCCGGCACGAGCCTGGTCGATCTGTCGGGGCTGCGCGTGTTCGTCGGC

GGCCCCATCCAGTACGCCCTCGGGCACGACAGCTTCCACCCACCGCTGCGCGACACGATCCAGGCCATCGTCACG

GCGGTGACCGAGGCGGGGGCCACCGTCTTCTCCGCCCATGTCGTCGAGAGGTTCGGCCGGGACACACCGCACTTC

TCGCCGGAGGACGTCAGCGCACGGGACCTGGACTGGATGCGCCGGTGCGACGTGTTCGTGCCCGTCCTGCCGGCG

GACGACGGTGGCGGAGTGATGCGCACCGACGGCACGCACATCGAGATGGGCTGGGCGTCGGCGCTGGGCCGTCCC

ATCGTCATGGTGACCCCCCTGCCGGTCCCGGCCGGGGCCAGCCATCTGCTGCGCGGGCTGCCGTCCGTGGCGGAC

GTCGGCGGCGTCGACCTGGCCGAGCTGCGCCGCGACGGCCCCGGTGAACTGCTGCTGCGGCTGGGCAAGGTCGGC

CGCGACGCGGTGGTGACACCATGA

> SPR_52930

MTTVSHAASATEVLGLRLVSPLVVGSGLLTDQERNIRRLLTGGAGAVVTKTIHPGPLPAGDERLLHLPTGMINST

TYSRRGVDSWCATLSRFADDDLPVIASVHADSPAALADLAARVADTGCRALELGISCLNEDGGLADSARRVADYT

GAVRRATPLPFSVKLAVGEQVGERVSAAVEAGADAITLSDTIAGLAVSPDTGEVLLGRPFGYSGAGIKPLVLAAI

YELRRGGLSVPVMGSGGVRSGTDVAEYLTVGADAVQVYTALHTHMHQTLAEIRGGFDTWLGARGGSVADVVGRAL

DGGRGEVRAAADHERHGLR

> SPR_52940

GTGAGGTGCGTGCGGCAGCGGACCACGAACGTCACGGCTTACGGTGATCTGACCAGTCCCGAGACACCCGCGGCG

CTGAGCGGCGCCACTCTGGTCTGGCCGGTGGGCGGCCTTGAGCAGCACGGCCCGCACCTGCCCCTGTCGGTGGAC

TACGACATTCCCGACGCGCTCGCCCGGCAGCTGGTGGCGGACGTCGACGGCGTGCTCTTCCCGGGCCAGCCGCTG

TCCGCCAGGTCACTGCCGCACAGCGGCGGCGGACTGCGCTTTCCCGGCACCGTCCACATCGACGGGGGAACCTTC

ATCGACTACGTCGCCCAGTGCCTGCGGGCACTGGGCAGGCTCGCTCCCGCCCGGCTGGTGGTCGTCAACGGGCAC

Appendix B

251

TACGAGAACGAGGCCCTGCTGTTCGAGGCGATCGACGGACTCGACCCGGCGCGCACCTTCCCCGCCACCGAGATC

GTCGCCTTCAGCTGGTGGAGCCTGGTGGAGGAGGACTGGCTGCGCAAGCGGCTGCCCGAATTCCCGGGCTGGCAC

GCCGAGCACGCCGGGGTGACCGAGACCAGTCTCATGATGTACCTGCGTCCCGAGGTGGTCCGCCCGGTGCGGGTG

GACCACCCCACTCCGCCCGCCGCCGGTGTGTACCGCCACCCCGTCGACGCGGCCCGCATGTCCACCCAGGGGGTC

CTCACCACGACCTCCGGTGCCAGCGGCGAGCTGGGGGAGGAGCTGTTCTGGCACGTGATGGACGGCGTGGCACGG

ACCCTCGCGGACAGCCCGTCCCCGCGCACCGAGAAGCGCGCAAGCGAGTGA

> SPR_52950

ATGCGCCCGCCGACGACCGAACGCGACGACTTCGAAGCCCGGCTGCAAAGCCTCTTCGGCGACAAACTCCGCCCC

GTGGAGGAGAGTTTCGAGGCCATCCAGCACTTCAAGGACGGTTCCTTCGCGGTGGGGCAGCTCGGCCTCATGCTC

TACACCAACGGATACAACCTGCGGGGCACCAGCACCCGTCATCCGAACGGAATGGTCTTCCACGACGGGCAGAAC

CTCTTCGGCGTAGGCTACTTCAGCAAGGAACAGGACGAGCGCAAGCACCTGCACATCGTCGCTCCCAAGGGCAAG

GACCGGGTCGCCGCGGTCAGGTCGTTCATCTCCGCGACCCGCGAGGCGGGCCTGGCACACACCTCCGTCTACGTA

CGCCACCTCTCGCCGGACGACCACGCGCTGTTCCTGGCGGCCGGCTTCGAGCCGGTGGCGGCGGACCCCTGGCAC

CCCGAGGCGCCGGAAGAGGACGAGACCTACCCCAACCGCGTCTACCGCCTGGACGATCTGCTGGCGGTGGACGCC

GACGGCCGCCTGGTGGTGAAGAACCTGGCAGGGGACGGCAACCGGCGTCACAAGAACAAGAACCGGCTCGCCTAC

CGGCGTTTTGAGAACTTCCTCGCCCGCAACGACCACCTGGAGCTCCGCATCCGTCCCTACGGATACGGCCCCGAC

GAGGCGAAGATGGCCAGGGGCGTGGTCGAGGGCTACTTCGAAGCCCGCCGGGCACAGGGCGAGGTCGTCGGCTCC

ACCCCCGAGGACTACACGGCGATCGTCACCCAGCGGCCCGGAGGCCGCAACGAACACGACTACTTCGCCTACCTC

GGCGTCCTGGCCCAGCAGGGCGGCGAGGAGGTGCCCGTGATGTTCTTCGCGGGCGAGCGCACCGCGCCGCACAGG

GCATCGCTGTACTGCACGATGTCGATGCGCTTCGCGGACCGTATGAGCGGCCTGTTCAAGGACGCCACGGGATTC

ACCGCGATTCCGCAGTACATCTGGCTGACCGTGTTCAAGAAACTGTGGGACCGCGGCATCCGTGAGGTCGACGCG

GGCGGATCCGAGGTCAAAGGCCTCGACGACCAGAAACGACAGTTGGGCGGACGGCCCGAAAAGACCCACTGGGTC

GTGGGCTGA

> SPR_52960

ATGCAATCGCGCACCGCGCACCAGGACTTCACACCGTTCGACGTCTGCGTCGTGGGGATGGGATACGTCGGCGTC

ACCCTCGCCGCCGCCCTCCTGTCCACCGGCAAGCGGGTGCTGGGCTACGAGAGCGACCCGGCCGTCGCGGGCGAC

CTGGCACAAGGCCGCCTGAGGCTGGCGGAACCCGGCGTCGCCGAGCTCATCGAGCGGGGAGCCGCCGACGGCACG

CTCGCGGTCACGGCCGACATCTGCGGGCACCGTCTGCCACCCGTCGTCGTCATCTGCGTCGGCACACCCATCGCG

CCGGGCGGCACGACGCCCGAACTCGGCCATCTGTCGGCCGCCGCCGAGGCGGTCGCCGCGGGAGCGGACGAGAAC

ACCCTGGTGATCGTGCGCAGCACCGTCCCCGTGGGCACCACCCGCGAACTGGTCCTGCCGGCCCTGGCCCGCCGC

GTTCCCCAGCCGCTGCTCGCCTTCTGCCCCGAGCGCACCATCCAGGGCAAGGCACTGGCGGAACTGCTGTCCCTG

CCGCAGATCGTCGGCGGTCTGACCGAAGAGGCAACGAAGCTGGCCGCGGGGTTCTTCACCACCGTCAGCGGGCGC

GTCGTCCCCGTATCCACACTGGAGGCCGCCGAGCTGGTCAAACTGGTCAACAACTGTCACACCGACCTCATCTAC

GGCTTCGGCAACGAAGTGGCCCTCATCGCCGAGAAGCTCGGCCTGGACGCCATGGAGGTCATCACCTCCGCCAAC

ACGGACTATCCGCGCCCCGATCTGAGCAGGCCCGGCTTCGTCGGCGGCAGCTGCCTCACCAAGGACCCCCACCTC

CTCGCCTACTCCCTCGCCCGCCACGACCACACCCCGCAGATGGTCATGGCGGCCCGCACCCTCAACGAGTCCATG

CCCCGCAGGGTCGGCGAGCGCGTGCTCGACGCGCTGCGCCGGGACGGCCAGGACCCGCAGCGGTCCACCGTCCTC

GTCTCCGGATTCGCCTACAAGGGCCGGCCCGAGACGGACGACCTGCGCGGCGCCCCCTGTGTGCCGCTGCTGGAG

TTCCTGCGCGGCAAGGTCGCCCGGGTGGTCGGGCACGACTTCGTGATCCCGCCCGAACGCATCGCGTCACTGGGC

GTACACCCCGTCACCCTCACCGAGGGGTTCACCGGCGCCCACGCCGCCATCCTGCTCAACGACCACGCCCGGTAC

GGCGAGCTGCCGGCCGACGAGCTCATCGCCCGGATGAGCCCGCCGGCGCTGGTGTACGACGCCTGGCGGGTGCTT

CCGCAGACGACGAAGACAATGAGGCTCGGCAGTGCCTGA

> SPR_52970

GTGCCTGAGAAGATCCTGGTCACCGGGGGAGCGGGGTTCATCGGGCTGCATCTGGCCGCGGAACTCGCCTCCCAC

CACGACGTCACCCTCCTCGACGACTTCAGCAGGGGCCGGCGCGACGCGTTGCTCGACTCCCTGCTCGACCGTGTC

ACGCTCGTCGAGCACGACCTGACCACCCCGATTCCCGACACCCTTCTGCCCGACGACTTCGACACCGTTCACCAT

CTGGCGGCCGTCGTCGGCGTAGTCCACTCCAACGAGGAACCGCAGCGGGTGCTGCGGACCAACCTTCTGTCCACC

GTGCACGTCCTGGACTGGTTCACCGGGCGGCCGGGCATGTCCGGCGCCACCTTCTGCTTCGCCTCCTCCAGCGAG

GCGTACGCGGGAAGCGTCGCGGCCGGTCTCGCCGCGCTGCCCACCGGCGAGGACGTCCCGCTGCTGGTCCCCGAC

CCCGAGGTACCCCGCTCCTCGTACGGCTTCAGCAAGATCGCCGGAGAGCTGCTCTGCCGCACCTACGCCCAAGTC

CACGGCTTCGCCCTGCGCATGGTGCGCTTCCACAACGTCTACGGACCGCGCATGGGCTACGAACACGTCATCCCG

CAGTTCATCGAGCGCGTCCTCGGCGGCGCCGACCCCTTCGCCGTCTACGGCGGCGACCAGACCCGGGCCTTCTGC

CACGTCGACGACGCCGTGGCCGCCCTGATGGCGCTGGCCGCGCTGCCCACCAAGGAGACCCTGCTCGTCAACATC

GGCAACGACCAGGAGGAAGTCCGCATGGACGACCTCGCCCGGATGGTCTTCGAGACCGCCGGGCGCCGGCCGCGC

ATCGCCGCGCACCCGGCACCGCCCCTGTCCCCGGTGCGCCGCCTGCCCGACCTGACCCTGCTGCGCGAACTCACC

Appendix B

252

GGATACCGCCCCTCGGTCGATCTGCGCGAGGGGCTGCGCCGCACCTACGCGTGGTACGCGCACGACCTCGCCTCC

CGTGGAGCGGGGCGGTGA

> SPR_52980

GTGAGCGGCATGCGGGTGCGGTACGTGCACCAGGGGTACTTCCCCGCGCGAGCGGGCGCCGAGCTGATGACCCGG

TCCCTCGCCGTGGCCATGAGCCGCCGCGGGCTGCGCGTGGGCCTGTACGGCGGCGAGGGGGACCCGGAGGACGAG

CGGCTGATGAAGGCCGCGGGGATCGGCGTCGAACCGCTGCCGGTCCGGGACGGCGAGGAGCGTGCGGCGGACCTG

GTGCACGCCGTCGACGCCTTCCAGCCCGAGAACATCAGGACCGGCCTGCGTCTGGCCCGGGCCTGGGGCGTGCCG

TTCGCCGTGACACCGGCCTCCGCGCCGGACGTGTGGCCGCACCGCGCCGCCGTACTGGAGGGCTGCCGCCGCGCG

GACGCCGTGTTCGTCCTGACCGACGCGGAGCGCGACATGCTGCGCGCCGAAGGCGTGGCGGACTCCGTCCTGCAC

CGGATCGGCCAGGGAGCGCACCTGCCGGGCACCGCCGACCCGGAGGGGTTCCGTGCCGCGCACGGCATCAGCGGG

CCCGTGGTGCTCTTCCTCGGCCGCAAGATGCGCTCCAAGGGGTACCGGGTGCTGCTGGAGGCGACGCGGCACGTC

TGGGCCCGCCACCCCGAGGCGCACTTCGTCTTCCTCGGCCCGCGCTGGGACGAGGACTGGGCGCAGTGGTTCGCC

GCCCACGCCGACCCCCGGATCACCGAACTGGACCGGGTGGACGAGGACACCAAACTCAGTGCCCTGGCGGCCTGC

GACCTGCTCTGCCTGCCCTCGACGGTCGACGTCTTCCCCCTGGTGTTCGTCGAGGCGTGGATGTGCGGCAAGCCC

GTGATCGGCTCCGCGTTCATGGGCAGCGCGGAAGTGATCGCGGACGGGCGGGACGGGCTGATCGTCCCGCCCGCC

GCCCGGCCGGTGGCGGACGCGGTCAGCCGCCTCCTCGCCGACCCGGCCGAACGGGCGCGGATGGGGCGCGAGGGC

CATGACAGGGCGCGCCGCGAGCTCACCTGGGACGCGGTCGCCGCACAGGTGCACCGCGTCTACACCGAACTGGTC

CCGGCCCGGAGTTGA

> SPR_52990

GTGAAAGCAGTCGTACTGGCCGGCGGCGAGGGGCGGCGCCTGAGGCCCGCCACCTTCACCGTCCCCAAGCCCCTC

ATCGAGGTCGACGGCACCCCGATCCTGCACATCATCCTGCGACAGCTCAGAAGCGCCGGATTCACCCAGGTCACG

CTCTCGCTGGGCTATCGCGCCCAGCTGATCGAGGCCAGCTTCGACGGCCCCCGCTGGGCGGGGCTCGACCTGCGC

TTCTCCCTGGAGCACGAGCCGCTGGGGACCGCCGGGCCGCTGGGTCTGCTCGCGCCGCTGGAGGACTCCACCCTG

GTGATGAACGCGGACCTGCTCACCGACATCGACTTCGCCGATCTGTTCAGGCGGCACAAGAAGTCCGAGGCGGCG

GCGACGATCGCCCTCGTTCCGCGCCATGTCGACCTCGCCCACGGTGTGGTGGAGCTCGACGGCGAGAACCGGGTG

GCCGGCTTCCGGGAGAAACCGCGTATGAGCTTCCTGGCCAGCAGCGGCATCTACGTCCTGGAACCCTCGGTCCTG

CGTCTGCTGCCCCGGCGGGCGCGTTACGACATGCCGGCGCTGCTCAAGGACGCCTCCGCCCGGGGCGAGCGCGTC

GAGGGCCATGTCCTCGACGCCGCCTGGCACGACATCGGCACCCCCGAACAGCTCGCGGCGGCCGACGCCGCGCTC

CGTGCCGACCGGGCGCGCTATCTGGGCGCCCTGGAGCGGCACGGCCCCGGTGCCGAAACGGACTCCACGGAGGAG

GCGGTGCGCGGATGA

> SPR_53000

ATGAGCGACTGGAAGATCCCCCTGTACGGGCCGAGCACCGGTGCGGCGGAGGCCCGCGCCGTCGCCGAGGTCCTG

CGCGCCAACTGGCTGTCCGTGGGCCGGGTGACCCAGGACTTCGAGGAGCGCTACGCGGCCGCGCTGGACGTCGAG

GACGCGATCGCGGTCAGCAGCGGGACCGCGGCGCTGCACCTGGCCGTCCTCGCTCTGGGGATCGGCCCCGGCGAC

GAGGTCGTCCTGCCGTCACTGAGCTTCGTCTCGGCGGCCGCCGTGGTCGCCCTGTGCGGGGCCACACCGGTGTTC

GCCGAGGTGAGCGGCGCCCATGACCTGTGTGTGGACCCGGCGGACGTGGCCGCCCGGATCACGTCGCGCACCCGT

GCCGTCGTGGCGGTGCACTACGGCGGCCATACGGCCGACCTGCCCGCCCTGACCGAACTGGCCCGGCGGCACGGT

CTGGCCCTCATCGAGGACGCCGCGCACGCTCCGGTCACCAAGACCGCGCACGGCGTCCTGGGCACGGTCGGCGAC

ATCGGCTGCTACAGCTTCTTCGCCACCAAGAACCTGGCCATGGGGGAGGGCGGCGCCGTCGTCGCCCGCGATCCC

GCGGTGCGCGCCCGGATCAGGCGGCTGCGCTCGCACGCGCTGACCGTGGGCGCCGAGCAACGCCACCGCGGCGGG

CCCTCGGCGTACGACGTGGACGGGTTCGGCCTCAACTACCGCCCCACCGAGATCGCCTGCGCCCTCGGTCGCGTC

CAGTTGGAAGCGCTGGCGGAGCGCCGCATCCTGCGCCAGGAGGCGGTGCGGGCCTATCGCACGCTGCTCTCGGGG

CTGCCCGGCCTGGAAGTGCCCTTCGCGGAGCGCCCGGTGGAGGAGGGCGCGCACCATCTGTTCCCGCTCGTGCTG

CCCGACGGCCTCGACCGCGAAGACCTCCAGGCGCAGCTGCGGGCGGCCGGTGTGCAGAGCGGTGTGCACTACCCG

CCCACCCATCTGTTCACCGCCTACCGCGAACGTTTCGGCACCCGCCCCGGCAGCCTCCCGGTCACCGAGAGCGTC

GCCGCCCGGCAACTGTCGCTGCCGCTGCACGCCGGGACCGGGCTCCAGGACGTCGCCCATGTGGCCGAGGCGGTG

AGCCGGACATGGCCGCCGCAGCGGTGA

> SPR_53010

ATGGCCGCCGCAGCGGTGAGCCCCGCCTGTGGCACCCGTCTCGTCGAGGGGGTGCTGCACCGCGACGGACGTCCC

CTGTTCTGCGTCGGCGTCAACTACTTCCCCTCGCGGGCGGGCTGCGACTACTGGCGGGACTGGGACCCGGCCGTC

CTCGACGCGGACTTTGCCCGTATGGCCGCGCTCGGCTTCAACACCGTGCGGATCTTCGTGTTCTGGGCCGACTTC

GAGCCCACCGAGGGCAGCTACGACCCGCGTATGACCGCCAGGCTGCGTGAACTGGCGGTCCTGGCGGAACGACAC

CACCTGCTGGTTCTGCCCTCGCTGCTGACCATATGGATGAACGGGCAGCTCTTCGACCCGCCGTGGCGGGCGGGC

Appendix B

253

CGGGACCTGTGGCGCGATCCGGTCATGGCCGAGCGGCAGCGCGCCTTCGTCGGGCACATCGCGGGCACGCTGCGC

CACGCGCCCAACATCCTCGCCTACGACATCGGCGACGAGATCCCGCACGTCGACCCGGCCGCGTCCCACTCGCTC

GGCGCGCACGAGGTACGGGCATGGTGGGCCGACCTCGCCGAAGCGATCCGGACGGCGGACCCGGGGGCTTTGGTC

CTCCAGGCCAACGAAGGCTCGGCGGTCTTCGGCGACCACGCCTTCCGGCCCGAGCACGCCCGGCCGCTGGACCTG

GTCGCGCTGCACGGCTTCCCGCTGTGGACCCCCTTCCACATCGAATCGGCCGCCGCCGAGAAGGCCACCGCCTAT

CTGCCCTACCTGGTGCGGCGCGGGCGGGCCCACGCCCCGGTGCTCGTCGACGAGATGGGCAGCTACGGCTGCGAC

GAGGCCACCGCGGCCCGCTATCTGCGCGCCGCGGCCCACAGTGCCTTCGCCGCGGGCGCCGTCGGTATCTGCGTG

TGGTGCTGGCAGGACTTCACCTCCGAGAGCAAGCCGTACGCACTGCGGCCCGGCGAACGCTTCGTGGGGCTGCTG

GACATGGACGGCCGCGAGAAGCCCGCCATGGACGCCTTCCGCGGCTTCGCGCGCCGGGTGACCGGGGAACTCGCC

GGTTTCCGCCCGCTGCCGGCCCGGGTGGGCGTGTTCCTGCCGGAGCGGGCCCGCGACCACGACGGCGGGTACCTG

GCGTCCKGGGCCGACACGGACGCCGCCGCCTTCTACGCGCACTGTCTGCTCCAACAGGCCCATCTGCCCTACGAG

TTCACGGGGACCGAGGACCTGGAGCGGTACGCGATGGTGATCTGCCCCTCCGTACGGCCCCTGCCCCTGGCCGCG

CAGCGACGGCTCGGCGAGTACACGGTCGCGGGCGGGGTGCTGCTGTACTCCACCGGCGATCCGCTGGGCTCGGCG

GGCCTGGAGGAGCTCTTCGGTGTGCGGATCCGGGACTTCACCCTGAACACGGCCGAGCAGGACCGCTTCACCTGG

GCCGACACCCCTTTCCCGGTGCACTGGCCCGCCGGACGTATCCCCGTGGTCGACAGCACGCTCGCCGAGACGCTC

GCCCGCTACCCCAACGGCGCGCCCGCGCTGGCCCGCCGGCAGCGGGGCGGCGGCGTCGCCTACTTCCTCAACGCA

CCGCTGGAAGCCCTGCTGAACGCGCCCTACCGGCTCCAGGAGGCGCCCTGGCACCGGCTGTACGCCGCGATCGGT

GAGAAGGAAGGCATACGGCCGGAGCTGTTCGCCGACGAGCCGCTGGTGGAGACCACCGTCCTGGCGCGCGGCGAC

GAACGCCGCGGTGTGGTCGTCAACCACGCCACCGCGCCCGTGACGACGACGGTGTACCGCACGTCCGCCGCCGGA

GATCCACGGGCGGTGCGGCACCTGAGCCTGGAGCCCAAGGGCGTCGCGCTCGTGCGCTGGCACGACGGACCGCCC

CCACACCCCGCCGCCACGGGCTCCACAGCCGGGCAGGACGGCGAGCAATGA

> SPR_53020

ATGATCATCGACGCCCATGTCCACGCCGGTGAGTACTACCGCCACTTCACCGCCCGCTTCGCCGACCAGATGATG

GCCACCACCGGTCTGCCCCCCGAGGCGCTGTCCGCGCCGGAGGACAAGCTCCTGGCGGAGATGGACGCCGCCGGG

GTGGACCACGCCTTCCTGCTCGCCTTCGAGGTGCGGCGCGTCGAGGGGTTCTCGGTGCCGAACACCTTCGTCGCC

GAGCTGTGCGCCCGCCATCCCCAGCGGTTCACCGGCTTCGCCTCGGTGGACGCGGGCCGGCCCGGCGCCGCCGAG

GAACTACGCCACTCCGTGACCGAACTGGGCCTGCGCGGGCTGAAGACGGCCCCCTGCTACCTGCGGATGTCCCCG

GCCGACCCCCGCTGGTTCGAGGTGTACCGGACCGCCCAGGACCTGGGCATCCCGGTCCTCGTCCACACCGGCTAC

ACCCCCGCCAAGAACGCCGACGCCCGCTTCTTCTCCCCCTTGCTGCTGGAGCCGGTAGCGAAGCGGTTCCCGGAA

CTGCGGCTGATCCTGGCGCACTTGGGCACCCCGTGGACGGCCCAGTGCATCGATCTGCTCGCCCGCCATCCCCAT

CTGTACGCGGACCTGTCGATCTTCGGCTCCTACCAGTCGCCCCCCACGGTGGCCGCGGCGCTCGCCCACGCCCGC

GAACGGGGAGTGCTGGACCGCCTCCTGTGGGGCACCGACTTCCCCTTCGCCACCATGTCCGCCGCCGTGGCCCGG

ATGACCCGTCTCACCACCGACGCCGCGCCGTGGCCGTCGGACAGCGCCCCGCTGACACCCGACGAACACCGGGCG

GTCATGGGCGGCACCGCCGCACTACTGACCCAGAAATGA

> SPR_53030

GTGGCCTTCATCCAGGGATACGAATTCGACGCCATGTCGCGCCGCCCCCTGTACGGGGACGTGACCCAGCGGCTC

GTCGACCTGTGCGCGTGCGCCCCCGGCAGCGTCGTCGCGGACGTCGGCTGCGGATCGGGCCTGGCCACCGAGCTG

CTGCTGGAACGGTTCCCGCAGCTCGGCTCCGTGGTGGGCATCGACCCCTCCGACCACGAACTGGCCCTGGCCAAG

GAGCGGCTGCGGCACCACCCCCGGGCCCGCCTGGTCACCGGCCGGGCCCAGGACGTGGGCGCGATCGTCGGGCCG

GTGGACGCCGTGGTGCTCAGCAACGTCATGCACCAGATCCCCAGGGCCGAGCGCCCGGCAGTGCTGCGCGGCTGC

CACGATCTGCTCGGACCCGGCGGCCGGCTCGCTCTGAACACGCTGTTCTACGAGGGCGCCGTGCTGCCCGAGAGC

CGCCGCTTCTACGCCGCGTGGCTGCACGCCACCCGGACGTGGCTGCGCAGCCGGGGCGGCGACCTGGTGCTGGAG

CGGGAGGCCCCCATCGCCCTTGAGACCCTGACCCCGGCCGACCACGAAGCCCTCATGGCCGAGGCGGGCTTCGCC

TCCGTACGGTCCGAGGAGGACGTCTACCCGTGGACCCTGGAGGACTGGCAGGCCCTGTGCGGATACTCGGTCTTC

GTCGAGGGCGCCACCGGACTGACGGATGTGGACCTCGGCTCCCGCGCGCTGACGGCCGCCCTGCACACCGTCTTC

CGCGAGCTGGGGCTCAGCAGCGTGCCCCGGCGCTGGCTGTTCGTCCACGGCACGAGGCAGGGGTGA

> SPR_53040

GTGATCGCGGCGACGCGGCCCGCGGTGGGCACCGCCACCGGGCCGCTGTCCCACGCCCAGCTGGGCATGTGGTTC

CTGGAGCGGCGCGCGGGAACCACCTTGTACGCGGAACCGATGACCTTCCGCCTGGTCGGCGAGGTGAACGTGCGC

GCCCTGCACGCCGCGGTCGAGGAGGTCGTGCGCCGCCACGACGCGCTGCGCACCCGTTTCACCGTGGTCGACGGA

GCTCCCCGCCAGCACGTCGTCCCCGACGCGACGGTACCGATGGCCCGGATCGACCTGGCGTATCTGCCCCCCGCC

CGGCGCCACCAGCGCGCCGAGCGGCTCCTGCGCGCCGAGCTCGGCCGGCCCATCGACCTCGCCCAGGGACCGCTG

GCGCGGGCCACCCTGATCCGGCTCGCCCCGCACGAACACGTCTTCCGCCTCACCCTGCACCATCTCGTCTGCGAC

GCCTGGTCGTGGTGGATGGTCGTCCTGCGCGAGCTGGAGGAGGGCTACACCCGCCGGGTCCGCGGCGGGCACGCG

CCCCTGGAGCCCGTCCGCACCCACTACGCGGACTTCGTCGACTGGCAGGGACGGTGGCTTCAGAGCCCCGCGCAC

Appendix B

254

ACCCGGCAGGTCGCCCACTGGCGCCAGGCCCTCGCCGGTGTCGCCCCACTGCCCGAGCTCACCCTGGCCCGTACG

ACCGCGCCGGTGCCGTACACCTCCTCCGCGACCGAGTGGACGGCCTTCCCGCAGCCGCTGCACGACCGGCTGCGT

GCCCTCGGCCGCCGCGAACACGTCACCCTGTACATGCTGCTGCTCACCGCCTTCACGCGGGTGCTGCGCCGCCAT

GTGCCGGTGGACGACATCCTGGTCGGCACCCGGGGCGGGTTCCGCAGCCGGCCCGAGTTCGAGAAGACCGTCGGC

CTGTTCGTCAACATGCTGCCCATCCGCACACGTGTCACCGAGGGCACCGGGTTCCGCGAGCTGCTGCCGCGGGTG

CGCGACACCCTCCTGGGCACGTATCTGAACCGGGACCTGCCCTTCGAACGCCTCGTGGCCGAGCTGGGCCTGCGC

CGGACCGGACCCCGGCCGGTGATCAACGTGTGCGTCTCCTTCCAGACCACCCCCGAGGTCATGCCGCGACTCCCG

GGCCTGGACGTCACCTTGCTCAACCACGACCCCTACTCGCCGTTCGACCTCGATCTCGGCTTCTACACCGAGGAC

GGCGGGCTGCGCGCCCTGATGATCTACAACCCGGCCCGGTACACCCGCGACGCGGTGCGGCACCTGCTCGACGCG

CTGCACCGGGAGCTGTGGGACGCCACCCGCGCACCCGGGCCCGTCCGCGCCGACGACGAGAAGGAGACCACCGTA

TGA

> SPR_53050

ATGAGGGCTTTGCAGTGGCACGGCGCCCACCGGGTGGCCCTGACCGACGACGCCCCGCCGCCGCGCGTCGAGACA

CCGGACGACGCGGTCGTACGGGTGGTCAGAAGCGCGATCTGCGGCACCGACCTGCACCCCTACCGGGGCGAGATA

GCCTCCTTCACTCCGGGCACCGTCACCGGCCACGAGTTCACCGGGGTCGTCGAGTCCGTCGGCTCCGGGGTGCGC

GGCCTGCGGCCGGGACAGCGGGTCGTGGCCTCGGACATCATCGCCTGTGGCCGCTGCTGGTGGTGCCGGCACGGC

GGGCACTACCAGTGCGAGCAGGTGGGACTGTTCGGCTACGACACGGTCGTGGGCGCGCGCCCGTTCGCGGGCGGC

CATGCCGAGCTGGTCCGTGTCCCGTTCGCCGATGTGGTCCTCTTCCCGATCCCCGACGACGTCGGCGACGAGCGG

GCGCTGCTCATCGGGGACGCGCTGGCCACCGGGTACGCCTGCGCCCTGGGCGGCGAGGTGCGCCCCGGCGACACC

GTCGCGGTGATCGGGTGCGGCGCGGTGGGTCTGCTGGCGGCCGAGGCCGCCCGGCTGCTGGGAGCCGCCCGGATC

CTGGCCGTCGACCCCGTCGAGGCCCGCCGCAAAGCGGCCGCCGAGCGCGGTGCGACGGCCCTGGCCCCCGGGGAC

GACCTCTCGGAGCGGGTGCGCGAGCTGACACGGGGACGCGGCGCCGACGCCGTCCTTGAGGCGGTCGGCACGGAC

GCCGCCCTGCTGAGCGCGCTGGAGATCGTACGGCCGCGCGGCGCGGTGTGCGCGGTCGGCGCCCACGCCTCCACG

GCGATGCCGCTGCCGACCATCCAGGCCTTCGCGAAGGAGGTGACCCTGCGGTTCGCCGTGGGCGACCCCATCGCC

ACGCGTGAGCCGCTGATGGAGCTCGTCCGCCAGGACCGCGTCGACCCCTCCTTCGTCATCACCCACCGCCTGCCG

CTCGCCGAAGCCCCCGAAGCCTTCCGGCTGTTCGACGCCGGCGAGGCCATCAAGGTGGTGCTCGTCCCGTGA

> SPR_53060

GTGACCACCCGGCTCCCCGCGTCACCGGCGCGCCCGCCCGCCCCGGATCCGCTCGACGGCGCCGTTCACCGTCTC

GTCGAGGAGCGGGCCGCGCGCACACCGGACGCCGACGCCGTGCTGTGCGGGACCGAACGCCTCAGCTATGCGCAG

TTGGACCTGCGGGCCGAGCGTCTCGCACGCCGCCTGCGCCGCCACGGAGTGGGCCCCGAAGTCCCGGTGGGTGTA

CATCTGACGCGCTCGCCCGAACTGGCGGTGGCCTGTCTGGCGGTGCTCAAGGCGGGCGGGGCCTGCCTCCCGCTG

GACCCCGCCCATCCGCCCGGCCGTCTGGCCGACGCCCTGCGCGACGCCGGTGCCCCGCTGGTCCTGAGCCGGCGC

GCCCTGGCGGCGGGCCTGGGCCCGCACACGGCAGCCGTCCTCTACACGGACTCGGAGGCTGACGACTCGTCAGCC

CACGAGCGTCCGGCGCCCGGCCCGGCGGCAGGATCGCCGTCACCGGGTGCCCCGGCAGCCGAGGACCGGCGAGCG

GAGGAGCGGCCGGGCGACGCGGGGGCACCCCCCGCCCCGCCTCTTGCACGCCGCCTCGCCTGGGTCGCGTACACC

TCGGGATCCACCGGCCGACCCAAGCCCGTCGGCCTCGAACACGGGCCGCTCGCCAACCTCGCCGTGCAGATCGGC

CGCCGTCTGGACCTGGGCCCCGACGACCGCGTGCTGCAGTTCGCCTCCATCGGCTTCTCCGTCGCGGCCGAGGAG

ATGTTCTCGACCTGGGCCGCCGGAGCCTGTCTCGTCATCGATCCCGACGACACCCTCGCCGACAGCGCGGGGCTG

CTCACCGCCGTGGACAAGTACGCCGTCACCGTCCTCCAGCTCACCCCGTCCCTGTGGTACGAGTGGCTGCGCGAG

CTGAGCCGGGACGGCACTCTGCGCCCGCCCGCCTCGCTGCGGCTGCTCGTGGTGGGCAGCGAGCAGGCCGCACCC

GACCGGGCGGCCGACTGGCTGGCCACCGGGGTGCGCCTGGTGCACGAGTACGGTGCCACCGAGGGCACGGTCTCC

CAGCTGCTGTACGAACCCGACGTGTCACCGGCCGAGTTGAGGACCTGGCCGCGTCTGCCCGTCGGTACGCCGTTG

CCGGGTGTCCGCGTCCACATCCTCGACGCGCGGCGCCGACCGGTCCCCCCGGGCGAGCCCGGCGAGCTCCACCTC

GCCGGAGACACCCTGGCGCGCGGCTACCTGGGGCAGCCCGAGCTCACGGCCGAGCGCTTCCTGCCCGACCCGTTC

GCCGATCGGCCCGGCGCGCGCATGTACCGCACGGGCGACCTCGCACGACAGCGTGCGGACGGCACCATCGAGTTC

CTGGGTCGCGTCGACCACCAGATCACGCTGCGCGGCCTGCGTATCGAGCCGGGCGAGGTCGAGTCGGCGATCGGC

CGGTACCCCGGCGTCACCGAGAGCGCCGTGCTGGCCCGCACCACCGCACGGGGCGACGATCAGCTGTGCGCGTGC

GTGGTGTGGGAGAAGGAGCGCGACGAGGCCGGGCTGCGCGCCCACCTGCGCGCCGCGCTCCCGCCCGCGCTCGTC

CCCGCCCGCCTGCTGGCCCTGCCCGACCTGCCGCTGACCCCCCATGGCAAGGTGGACCGCCAGGCCCTGCGGGCC

CTGCGCTGGGAACCCGACCCCGTCGATTCACGGGGCGAGGCGCCGCGCACCGCGCTGGAGGCCGCCCTCGCCGCG

CTCTGGGCCTGGACCCTCGACGTGTCCCGGATCGGCCTCGACGACAGCCTCTTCGACCGGGGCGGCGACTCCCTG

ACCGCCACCCGGCTCGCGGCCCGACTGCGCGACGTCCTGATGGCGGACGTACGGCAGCGGACCGTGTTCGACGCG

CCGACCGTACGGGCCATGGCCGAGGTGATCTCGCGACAGCGCCGCCGCGCTCGCGCCGACGAGCCCGTGACGGCG

CCGGACGCGTACGAGGACGCCCCACTGACGTCGGCGCAGTGGCGCATGTGGCTGCACCACCGCAGATCCCCGACG

AGCGCCGCGTATCACGAACCCGTGGCCCTGCGGCTACGGGGCCCGCTCGACCCCGACCACCTCGTACGGGCACTG

CGGCGGACGGTGGGGCGGCATGCGGCTCTGCGCACCACCCTCGCCACGGCGGCGGGGCAGCCGCTCCAGCGGGTC

GCGCCGCCCGCCACCGCCGAGGCGTTCCCCCTGGCCCGCTTGGACCTGAGCGGCCACGCGGAGGGTGAACTTGAC

Appendix B

255

CGAGTGGTCGAGGAGTTGGCCGTGGCGCCGTTCGACCTGCGGCGTGGCCCCCTGATCCGCGCGCACCTGCTGCGG

GTCGCGGCCGACGAGCACGTCCTCGTGCTGGTCCTGCACCACATCGTCTTCGACGGATGGTCGATGGACGTGCTC

TTCCGGGATCTGGCGGCCTTCCACGACGAGGCCGCGACCGGAGTCGCCGCCGCGCCGGCGCCCCTGCCCTCCTCG

CCGCCCGCGCGCCCTCCGCTGCCCGCGGACGACCCGGGCGCCGAGCGCCGCGCCCAGGAACAGCGCGCGTACTGG

AAAAAGCAGCTGGCGGGGGCACCGCCCGTCACACGGCTGCCGACCGGCCGACCCACGTCCCGGCAGGGCACGGTG

CACTGCCCGTTCACCGTCCCGGCGGCCACCGCGGCGCGGCTGCGCGAGCTGGCGGCGGAGGAAGGCGCCACCCCG

TTCATGGTGATCCTCGCCGTCTTCACGGCAGTCGCCCACCAGAGCTCCGGCGCCCGCGACATCGTGGTGGGCACG

CTGCTGGCAGGCCGCGACGACCCGGACACCGCCGACCTGATCGGTCTGTTCACCCACACCGTTCCGCTGCGCACA

CAGGTGCCCGAGGGGACGACGGTCCGTCAGCTGGTGCGGCGGGTACGTGAGACGGTTCTGGGCGCGGTGGCCCAT

CAGGAGGTGCCGTTCGAGGACATCGTGGCGCACCTGGGACCGCCACGGGATCCCCGGCACAACCCGGTGTTCCAG

ATGGTGTTCTGCCACGGCGCCGCGTCCGCCCGCGCCCCGCAGCTGCGCGGCCTGAGCGTGACCCCCGTGGAGGTC

GCCGTGCCCTTCGCCAAGTTCGACGTCACCGTCATGGTCGACGAGGACCGGCACGGCGGATACGCCATCGACCTC

GCCTACGACCTCGCGCTCTACGACGAGACGACCGCTCACCGCCACACCGCGGCGTTCCGGTCCCTGCTGGAAGCC

GCCGCGGACCGACCGGAAGCAGGGGTGTGA

> SPR_53070

GTGTCCACAGAATCGACCGCCCGCACCACCGAATCCCCGGCCGCCGCCGCCCCGACGAACGCCGACGCACCCCCG

ACGCCCGAGGCCGCGTCGGTCCGGGTGGCCGAATCGGTTCGCCGGATCTGGGCCGAACTCCTGCAGATCGACGTC

GAAGCGATCGACGTCCGCCACAGCGACTTCTTCGAGCTCGGTGGCTATTCACTGCTCGCGCTCCAGGCCATCGGC

AGGCTGCTGGAGGAGCGGGGCTTCGACGAGTTCGAGGCGGCGGAGCTGGAGGGCGCGTTGCTCAACCGCCTCTTC

GAGGAGCCCACACCGTTGGCCCAGGCGGAGTGCCTGCAGTCCGCGCTGGCCGCCGGCGGGGCACCGCGCGCGTGA

> SPR_53080

ATGCACCACCGCTCCAAGGCCCTGTACGGGGTTTTCGTCACCGTCCTCGGACTCACGCTGACCGCCTGCGGCGGT

GACGGAGGAGGCGGGAAGTCCGGTGTTTCCGAGGGCGGGGCGGCGAAGGGCGAGACCGGCCAGGAAACCCCGTCC

GCGAGCCCGTCCGAGAAGCCGGAGTGGGGCCCCGCGCTGGCGATGGGCCAGCCGGCCCCGAAGCTGTACGAACCC

CTGAACACCAGCGGCGGGAAGTTCCAGGTAACCGCCAAGAAGATCGTCAAGGGAACTCCCCAGCAGGCAAAGGAC

CTGAACTGGGACACGCTCGCCCCGGGCGAACTCAAGGGCAGTACGCCGTACTTCGTGTACTTCACGTACACGCTC

AAGGAAGGCAAGCCGCAGGTCGCCAACCCTGACCTCGGGGCGCATGCCGCCGCCCTCGACATGAAGGGCGTGAAA

GTCGCGGAGCGGCCGGTCGTCCACTCGGGATTCGTCGACGGCGGTTGCGAAGTCCCACCCGTATACATGGGCTGG

GACATCGGCGAGACCCACACCCTCTGCACGGTCTTCGCCGGGGACGAGGCGCATCCCCCTGCCCGACTGGCCTGG

GGTACGGACATAGAAACCGACACGGACTACATGAAGGCCGCATCGTGGAAGTGGACCACCCAGTGA

> SPR_53090

ATGCCCGGTATGCGTGCGTTCTTCACCGTTGATCAGCGGCGGTTGTCGTTCGTGGACTTCGGCGGCCCGGGGCTC

CCGTTGCTGGCGTTTCACGGGCATTACAACGAGGCATCGGTGTTCGCCCCGCTGGCTGAAGCGCTGGCGCCGCAG

TGGCGGGTGATTGCCCTGGACCAGCGTGGGCATGGGGAATCCGACCGCGCCCCGAGCTACCAGCGGTCCGAGTAC

GGCGCTGACATCGCCGCCTTCCACCGCCATCTGGGACTCGGTCCGGTGGCGGTACTCGGGCATTCCCTGGGCGGC

GTGAACGCCTATCAGTACGCCGTCCGGCACGCGGACCGGGTGACAGCCCTGATCGTCGAGGACGTCGGCGCCGTG

GTGGATGCCGACTGGTCGCTCACCACGCAACTGCCTCGCAGAGCACCCTCCCGTCGGGCACTGGCCTCGGCTCTC

GGCCCGCTGGCGCCCTATCTCGAATGCACCTTCCGTCAGTTCGGTGACGGCTGGGGATTCTCCTTCGACATCAAG

GACACGGTGCTGTCCCACGAAGCCCTCACCGGGGACTACTGGGGCGACTGGGAGGCGGTGCCCTGCCCGACCCTG

CTGATCCGGGGAAGGGACAGCGTCGTCCTGGCGTCGGACCACGCCCGGGAGATGATAGCCCGCCGGGCAGGTCAG

GCCGAGCTGGTCGAACTTCCGGCCGGACACGTCGTGCACTGCGACGCTCCCGACGAGTTCGCCGCCGCTGTGCGC

ACCTTCCTGTCCCAACTGCCCGAGAGGTGA

Appendix C

256

APPENDIX C

The nucleotide sequences of the DNA fragments used to make each of the knock-out constructs

within the genes they target are provided in this appendix. The black text represents the regions

of the target gene within the wild-type strain, while the blue and green text represents the

sequences of the target gene that were integrated into the genome of each mutant strain via

homologous recombination. The position of the pOJ260 sequence within the target gene of

each mutant strain is also provided.

> S. polyantibioticus ∆CIN

CCGCATCACCGGCCTGTACGTGGCCCCGCCGATCGTGCTCGCCCTCGCCAAGCACCCGGCGGTCG//CCCAGTAC

GACCTCTCCTCCGTGGAGTACGTCGTCAGCGCCGCCGCCCCGCTGGACGCCGGGCTCGCCGCCGCCTGCTCGGCC

CGCCTCAAGGTCCCGCCGGTGCGCCAGGCGTACGGCATGACCGAGCTCTCGCCCGGCACCCACGCCGTCCCCCTG

TCGGCACAGAACCCGCCGCCCGGCACCGTCGGCACACTCCTGCCCGGCACCGAGATGCGGCTGCTCTGCCTCGAC

GACCCCGGCCGCGACGCCGCCCCCGGCGAGCGGGGCGAGATCGCCATCCGGGGCCCGCAGGTCATGAAGGGCTAC

CTCGGCCGCCCCGAGGCCACCGCCGAGATGATCGACGCCGAGGGCTGGGTGCACACCGGCGACGTCGGCCACGTA

GACGCCGACGGCTGGCTGTTCGTCGTCGACCGCGTCAAGGAGCTCATCAAGTACAAGGGCTTCCAGGTCGCCCCC

GCCGAACTGGAGGCGCTGCTGCTCACCCATGACGCCGTCGCGGACGCGGCGGTGGTCGGGGTGTACGACGAGGAC

GGCACCGAGGTGCCGTGCGCCTATGTCGTACGGGCACCCGGCGCCCCGGACCTCACCGCCGAGGACGTCATGGCG

TACGTGGCCGAACGCGTCGCCCCGTACAAGAAGATCCGCCGCCGC//pOJ260//GCCCAGTACGACCTCTCCTC

CGTGGAGTACGTCGTCAGCGCCGCCGCCCCGCTGGACGCCGGGCTCGCCGCCGCCTGCTCGGCCCGCCTCAAGGT

CCCGCCGGTGCGCCAGGCGTACGGCATGACCGAGCTCTCGCCCGGCACCCACGCCGTCCCCCTGTCGGCACAGAA

CCCGCCGCCCGGCACCGTCGGCACACTCCTGCCCGGCACCGAGATGCGGCTGCTCTGCCTCGACGACCCCGGCCG

CGACGCCGCCCCCGGCGAGCGGGGCGAGATCGCCATCCGGGGCCCGCAGGTCATGAAGGGCTACCTCGGCCGCCC

CGAGGCCACCGCCGAGATGATCGACGCCGAGGGCTGGGTGCACACCGGCGACGTCGGCCACGTAGACGCCGACGG

CTGGCTGTTCGTCGTCGACCGCGTCAAGGAGCTCATCAAGTACAAGGGCTTCCAGGTCGCCCCCGCCGAACTGGA

GGCGCTGCTGCTCACCCATGACGCCGTCGCGGACGCGGCGGTGGTCGGGGTGTACGACGAGGACGGCACCGAGGT

GCCGTGCGCCTATGTCGTACGGGCACCCGGCGCCCCGGACCTCACCGCCGAGGACGTCATGGCGTACGTGGCCGA

ACGCGTCGCCCCGTACAAGAAGATCCGCCG//GGTGGAGTTCGTCGCCGGGGTGCCGCGCGCGGCCACCGGGAAG

> S. polyantibioticus ∆LAC

GGAGCACGGTCTGCGCGGCACCCCGTACGGGCACTTCGGCGACGGCTGTGTCCACGTCCGGATCG//ACTTCGAC

CTGCTGAGTACGGCGGGTGTGGCGCGCTTCCGCCGGTTCTCCGAGGAGCTGGCGGACCTGGTGGCCGCGCACGGC

GGCTCGCTCTCCGGCGAGCACGGTGACGGGCAGGCGCGGGCCGAGCTGCTGCCGAGGATGTACGGGGACGAACTG

GTCGGGCTGTTCGGGCGGTTCAAGGACGTGTGGGACCCGTCGGGCCTGCTCAACCCCGGGATGCTGGCCCGTCCG

GCCCGGCTGGACGAGAACCTGCGCTTCGCGGTGCTGCCGAAGGGGCCGGTGGAGGTGGAGTTCGGCTATCCGCAG

GACGGCGGGGACTTCTCGGCGGCGGTACGGCGGTGTGTCGGGGTGGCCAAGTGCCGTACTGTGTCCGGGACTTCG

GGTTCGTCGGTGATGTGCCCGTCCTTCCGGGCCACCGGCGAGGAGGCGCACTCGACGCGGGGCCGGGCGCGGCTG

CTGCACGAGATGCTGGCGGGCGAGGTCGTCACCGGCGGCTGGCGCTCGCCGGAGGTGCGTGACGCGCTCGATCTG

TGCCTGTCCTGCAAGGGCTGCCGCAGCGACTGCCCGGTCGGGGTGGACATGGCCACGTACAAGGCGGAGTTCCTG

CCGC//pOJ260//GACTTCGACCTGCTGAGTACGGCGGGTGTGGCGCGCTTCCGCCGGTTCTCCGAGGAGCTGG

CGGACCTGGTGGCCGCGCACGGCGGCTCGCTCTCCGGCGAGCACGGTGACGGGCAGGCGCGGGCCGAGCTGCTGC

CGAGGATGTACGGGGACGAACTGGTCGGGCTGTTCGGGCGGTTCAAGGACGTGTGGGACCCGTCGGGCCTGCTCA

ACCCCGGGATGCTGGCCCGTCCGGCCCGGCTGGACGAGAACCTGCGCTTCGCGGTGCTGCCGAAGGGGCCGGTGG

AGGTGGAGTTCGGCTATCCGCAGGACGGCGGGGACTTCTCGGCGGCGGTACGGCGGTGTGTCGGGGTGGCCAAGT

Appendix C

257

GCCGTACTGTGTCCGGGACTTCGGGTTCGTCGGTGATGTGCCCGTCCTTCCGGGCCACCGGCGAGGAGGCGCACT

CGACGCGGGGCCGGGCGCGGCTGCTGCACGAGATGCTGGCGGGCGAGGTCGTCACCGGCGGCTGGCGCTCGCCGG

AGGTGCGTGACGCGCTCGATCTGTGCCTGTCCTGCAAGGGCTGCCGCAGCGACTGCCCGGTCGGGGTGGACATGG

CCACGTACAAGGCGGAGTTCCTG//CACCACCACTACCGGGGCCGGCTGCGCCCCGCCTCCCACTACGCGATGGG

> S. polyantibioticus ∆THI

ATGCCCGG//TATGCGTGCGTTCTTCACCGTTGATCAGCGGCGGTTGTCGTTCGTGGACTTCGGCGGCCCGGGGC

TCCCGTTGCTGGCGTTTCACGGGCATTACAACGAGGCATCGGTGTTCGCCCCGCTGGCTGAAGCGCTGGCGCCGC

AGTGGCGGGTGATTGCCCTGGACCAGCGTGGGCATGGGGAATCCGACCGCGCCCCGAGCTACCAGCGGTCCGAGT

ACGGCGCTGACATCGCCGCCTTCCACCGCCATCTGGGACTCGGTCCGGTGGCGGTACTCGGGCATTCCCTGGGCG

GCGTGAACGCCTATCAGTACGCCGTCCGGCACGCGGACCGGGTGACAGCCCTGATCGTCGAGGACGTCGGCGCCG

TGGTGGATGCCGACTGGTCGCTCACCACGCAACTGCCTCGCAGAGCACCCTCCCGTCGGGCACTGGCCTCGGCTC

TCGGCCCGCTGGCGCCCTATCTCGAATGCACCTTCCGC//pOJ260//GTATGCGTGCGTTCTTCACCGTTGATC

AGCGGCGGTTGTCGTTCGTGGACTTCGGCGGCCCGGGGCTCCCGTTGCTGGCGTTTCACGGGCATTACAACGAGG

CATCGGTGTTCGCCCCGCTGGCTGAAGCGCTGGCGCCGCAGTGGCGGGTGATTGCCCTGGACCAGCGTGGGCATG

GGGAATCCGACCGCGCCCCGAGCTACCAGCGGTCCGAGTACGGCGCTGACATCGCCGCCTTCCACCGCCATCTGG

GACTCGGTCCGGTGGCGGTACTCGGGCATTCCCTGGGCGGCGTGAACGCCTATCAGTACGCCGTCCGGCACGCGG

ACCGGGTGACAGCCCTGATCGTCGAGGACGTCGGCGCCGTGGTGGATGCCGACTGGTCGCTCACCACGCAACTGC

CTCGCAGAGCACCCTCCCGTCGGGCACTGGCCTCGGCTCTCGGCCCGCTGGCGCCCTATCTCGAATGCACCTT//

CCGTCAGTTCGGTGACGGCTGGGGATTCTCCTTCGACATCAAGGACACGGTGCTGTCCCACGAAGCCCTCACC

> S. polyantibioticus ∆A99

GGAGCGGCCGGGCGACGCGGGGGCACCCCCCGCCCCGCCTCTTGCACGCCGCCTCGCCTGGGTCGC//GTACACC

TCGGGATCCACCGGCCGACCCAAGCCCGTCGGCCTCGAACACGGGCCGCTCGCCAACCTCGCCGTGCAGATCGGC

CGCCGTCTGGACCTGGGCCCCGACGACCGCGTGCTGCAGTTCGCCTCCATCGGCTTCTCCGTCGCGGCCGAGGAG

ATGTTCTCGACCTGGGCCGCCGGAGCCTGTCTCGTCATCGATCCCGACGACACCCTCGCCGACAGCGCGGGGCTG

CTCACCGCCGTGGACAAGTACGCCGTCACCGTCCTCCAGCTCACCCCGTCCCTGTGGTACGAGTGGCTGCGCGAG

CTGAGCCGGGACGGCACTCTGCGCCCGCCCGCCTCGCTGCGGCTGCTCGTGGTGGGCAGCGAGCAGGCCGCACCC

GACCGGGCGGCCGACTGGCTGGCCACCGGGGTGCGCCTGGTGCACGAGTACGGTGCCACCGAGGGCACGGTCTCC

CAGCTGCTGTACGAACCCGACGTGTCACCGGCCGAGTTGAGGACCTGGCCGCGTCTGCCCGTCGGTACGCCGTTG

CCGGGTGTCCGCGTCCACATCCTCGACGCGCGGCGCCGACCGGTCCCCCCGGGCGAGCCCGGCGAGCTCCACCTC

GCCGGAGACACCCTGGCGCGCGGCTACCTGGGGCAGCCCGAGCTCACGGCCGAGCGCTTCCTGCCCGACCCGTTC

GCCGATCGGCCCGGCGCGCGCATGTACCGCACGGGCGAG//pOJ260//TTAAGTACACCTCGGGATCCACCGGC

CGACCCAAGCCCGTCGGCCTCGAACACGGGCCGCTCGCCAACCTCGCCGTGCAGATCGGCCGCCGTCTGGACCTG

GGCCCCGACGACCGCGTGCTGCAGTTCGCCTCCATCGGCTTCTCCGTCGCGGCCGAGGAGATGTTCTCGACCTGG

GCCGCCGGAGCCTGTCTCGTCATCGATCCCGACGACACCCTCGCCGACAGCGCGGGGCTGCTCACCGCCGTGGAC

AAGTACGCCGTCACCGTCCTCCAGCTCACCCCGTCCCTGTGGTACGAGTGGCTGCGCGAGCTGAGCCGGGACGGC

ACTCTGCGCCCGCCCGCCTCGCTGCGGCTGCTCGTGGTGGGCAGCGAGCAGGCCGCACCCGACCGGGCGGCCGAC

TGGCTGGCCACCGGGGTGCGCCTGGTGCACGAGTACGGTGCCACCGAGGGCACGGTCTCCCAGCTGCTGTACGAA

CCCGACGTGTCACCGGCCGAGTTGAGGACCTGGCCGCGTCTGCCCGTCGGTACGCCGTTGCCGGGTGTCCGCGTC

CACATCCTCGACGCGCGGCGCCGACCGGTCCCCCCGGGCGAGCCCGGCGAGCTCCACCTCGCCGGAGACACCCTG

GCGCGCGGCTACCTGGGGCAGCCCGAGCTCACGGCCGAGCGCTTCCTGCCCGACCCGTTCGCCGATCGGCCCGGC

GCGCGCATGTACCGCACGGGCGA//CCTCGCACGACAGCGTGCGGACGGCACCATCGAGTTCCTGGGTCGCGTCG

> S. polyantibioticus ∆CYC

GCGCGCCCTGCACGCCGCGGTCGAGGAGGTCGTGCGCCGCCACGACGCGCTGCGCACCCGTTTCAC//CGTGGTC

GACGGAGCTCCCCGCCAGCACGTCGTCCCCGACGCGACGGTACCGATGGCCCGGATCGACCTGGCGTATCTGCCC

CCCGCCCGGCGCCACCAGCGCGCCGAGCGGCTCCTGCGCGCCGAGCTCGGCCGGCCCATCGACCTCGCCCAGGGA

CCGCTGGCGCGGGCCACCCTGATCCGGCTCGCCCCGCACGAACACGTCTTCCGCCTCACCCTGCACCATCTCGTC

TGCGACGCCTGGTCGTGGTGGATGGTCGTCCTGCGCGAGCTGGAGGAGGGCTACACCCGCCGGGTCCGCGGCGGG

CACGCGCCCCTGGAGCCCGTCCGCACCCACTACGCGGACTTCGTCGACTGGCAGGGACGGTGGCTTCAGAGCCCC

GCGCACACCCGGCAGGTCGCCCACTGGCGCCAGGCCCTCGCCGGTGTCGCCCCACTGCCCGAGCTCACCCTGGCC

CGTACGACCGCGCCGGTGCCGTACACCTCCTCCGCGACCGAGTGGACGGCCTTCCCGCAGCCGCTGCACGACCGG

CTGCGTGCCCTCGGCCGCCGCGAACACGTCACCCTGTACATGCTGCTGCTCACCGCCTTCACGCGGGTGCTGCGC

CGCCATGTGCCGGTGGACGACATCCTGGTCGGCACCCGGGGCGGGTTCCGCAGCCGGCCCGAGTTCGAGAAGACC

GTCGGCCTGTTCGTCAACATGCTGCCCATCCGCACACGTGTCACCGAGGGCACCGGGTTCCGCGAGCTGCTGCCG

CGGGTGCGCGACACCCTCCTGGGCACGTATCTGAACCGGGACCTGCCCTTCGAACGCCTCGTGGCCGAGCTGGGC

CTGCGCCGGACCGGACCCCGGCCGGTGATCAACGTGTGCGTCTCCTTCCAGACCACCCCCGAGGTCATGCCGCGA

Appendix C

258

CTCCCGGGCCTGGACGTCACCTTGCTCAACCACGACCCCTACTCGCCGTTCGACCTCGATCTCGGCTTCTACACC

G//pOJ260//TTAACGTGGTCGACGGAGCTCCCCGCCAGCACGTCGTCCCCGACGCGACGGTACCGATGGCCCG

GATCGACCTGGCGTATCTGCCCCCCGCCCGGCGCCACCAGCGCGCCGAGCGGCTCCTGCGCGCCGAGCTCGGCCG

GCCCATCGACCTCGCCCAGGGACCGCTGGCGCGGGCCACCCTGATCCGGCTCGCCCCGCACGAACACGTCTTCCG

CCTCACCCTGCACCATCTCGTCTGCGACGCCTGGTCGTGGTGGATGGTCGTCCTGCGCGAGCTGGAGGAGGGCTA

CACCCGCCGGGTCCGCGGCGGGCACGCGCCCCTGGAGCCCGTCCGCACCCACTACGCGGACTTCGTCGACTGGCA

GGGACGGTGGCTTCAGAGCCCCGCGCACACCCGGCAGGTCGCCCACTGGCGCCAGGCCCTCGCCGGTGTCGCCCC

ACTGCCCGAGCTCACCCTGGCCCGTACGACCGCGCCGGTGCCGTACACCTCCTCCGCGACCGAGTGGACGGCCTT

CCCGCAGCCGCTGCACGACCGGCTGCGTGCCCTCGGCCGCCGCGAACACGTCACCCTGTACATGCTGCTGCTCAC

CGCCTTCACGCGGGTGCTGCGCCGCCATGTGCCGGTGGACGACATCCTGGTCGGCACCCGGGGCGGGTTCCGCAG

CCGGCCCGAGTTCGAGAAGACCGTCGGCCTGTTCGTCAACATGCTGCCCATCCGCACACGTGTCACCGAGGGCAC

CGGGTTCCGCGAGCTGCTGCCGCGGGTGCGCGACACCCTCCTGGGCACGTATCTGAACCGGGACCTGCCCTTCGA

ACGCCTCGTGGCCGAGCTGGGCCTGCGCCGGACCGGACCCCGGCCGGTGATCAACGTGTGCGTCTCCTTCCAGAC

CACCCCCGAGGTCATGCCGCGACTCCCGGGCCTGGACGTCACCTTGCTCAACCACGACCCCTACTCGCCGTTCGA

CCTCGATCTCGGCTTCTACACCG//GAGGACGGCGGGCTGCGCGCCCTGATGATCTACAACCCGGCCCGGTACAC

> S. polyantibioticus ∆ACY

ATGCCCTCGACCACTGAATCCGCCGCCACG//CTGTGGGAGCTCATCGACCGGGCCGTACGCCTCTCCCCCGCGG

CCACCGCCGTACGCCAGGGAACGCGGGCCCTCACCTTCCGCGAACTCGCCGACCGCGTCGAGACCACAGCACGCC

GCCTGCGCACGCGCCTGCCCGCCGACGGCGGAGGAACCGTGGGCCTGCTCTTCGAGAACACCGTGGAGAGCACGG

TGGCCTTCCTGGGCGCGCTGTACGCGGGCGTACCCCTCACGCCCCTCGAACCCGACAGCACCGAGCCCCATCTCC

TGGGCGTGCACCGGGACTTGGGACCCCTGCACCTCGTCGGTCGGCAGGCGAGGCTCAGCACACTGGCCCCTCCCG

CTGCCACCTCACTCGCCGCCCGGTGGCAGGGCGGTGTCCTCATCGACGTGGACGAGCTCACCGCCCGCCCCGGCG

CGGCGGCCCCGTCGGCGCCGCTGCCCGCGCCGCCGCCCGACGCCCCCGCGCTCTACCAGTACACCTCCGGCTCGA

CCGGCGAGCCGAGGGCCGCCGTGCACTCACAACACGACCTGGTCCGCGGTGGCGAGATCTACGCCCGCACCTACG

GCATCACCCCGGCCGACCGGATTCTCGCGGCCGTACCCCTGCTGCACTCCTTCGGCATGGTCGCCGCGCTCGCCA

CCGCGCTGCACGCCCGCGCGGAGCTCGTCCTGCTCGGCCGGTTCGCACCGGCCGAAATGCTCCGGGCACTGCACC

AGCACGCCTGCACCATCGTGGTGGGCACCCCGCTCGCCTATGACCTGGCGGCCCGTTCGGCGGCCTCGCGCAGCG

AGACGTCCCGCCCGGGCGACACCGTACGGCTCTGTCTGTCCTCCGGGGCGGCCCTGCCCCCGGCCGTGGCGGACC

GCTTCGCCCAGCACTGCGGCCCGGCCGTCCAGCAGGTCTACGGAAGCACCGAGG//pOJ206//TTAACTGTGGG

AGCTCATCGACCGGGCCGTACGCCTCTCCCCCGCGGCCACCGCCGTACGCCAGGGAACGCGGGCCCTCACCTTCC

GCGAACTCGCCGACCGCGTCGAGACCACAGCACGCCGCCTGCGCACGCGCCTGCCCGCCGACGGCGGAGGAACCG

TGGGCCTGCTCTTCGAGAACACCGTGGAGAGCACGGTGGCCTTCCTGGGCGCGCTGTACGCGGGCGTACCCCTCA

CGCCCCTCGAACCCGACAGCACCGAGCCCCATCTCCTGGGCGTGCACCGGGACTTGGGACCCCTGCACCTCGTCG

GTCGGCAGGCGAGGCTCAGCACACTGGCCCCTCCCGCTGCCACCTCACTCGCCGCCCGGTGGCAGGGCGGTGTCC

TCATCGACGTGGACGAGCTCACCGCCCGCCCCGGCGCGGCGGCCCCGTCGGCGCCGCTGCCCGCGCCGCCGCCCG

ACGCCCCCGCGCTCTACCAGTACACCTCCGGCTCGACCGGCGAGCCGAGGGCCGCCGTGCACTCACAACACGACC

TGGTCCGCGGTGGCGAGATCTACGCCCGCACCTACGGCATCACCCCGGCCGACCGGATTCTCGCGGCCGTACCCC

TGCTGCACTCCTTCGGCATGGTCGCCGCGCTCGCCACCGCGCTGCACGCCCGCGCGGAGCTCGTCCTGCTCGGCC

GGTTCGCACCGGCCGAAATGCTCCGGGCACTGCACCAGCACGCCTGCACCATCGTGGTGGGCACCCCGCTCGCCT

ATGACCTGGCGGCCCGTTCGGCGGCCTCGCGCAGCGAGACGTCCCGCCCGGGCGACACCGTACGGCTCTGTCTGT

CCTCCGGGGCGGCCCTGCCCCCGGCCGTGGCGGACCGCTTCGCCCAGCACTGCGGCCCGGCCGTCCAGCAGGTCT

ACGGAAGCACCGAG//GCCGGTGTCGTCGCCGCGCAGCTCCCGCAGCCGGACGGCACGGCCGATGCCGGGGTGGG

> S. polyantibioticus ∆PAAK

GGCGGTATGACGGCCCGCCAGGTCCAGCTGATCCAGGACTTCCGGCCCGAGGTCATCATGGTGACT//CCGTCGT

ACATGCTGACCCTCCTCGACGAGTTCGAGCGGCAGGGCGTCGACCCGCGCGCGACCTCGCTGAAAGTCGGGATCT

TCGGAGCCGAGCCGTGGACGGAGGAGATGCGCCGCGAGATCGAGGAGCGCTTCGCCATCGACGCGGTCGACATAT

ACGGGCTGTCGGAGGTGATCGGGCCCGGGGTGGCGCAGGAGTGCGTGGAGACCAAGGACGGGCTGCACATCTGGG

AGGACCACTTCTACCCGGAGATCGTCGACCCGCTCACCGGCGAGGTGCTGCCCGAGGGCGAGCGCGGCGAGCTGG

TCTTCACCTCGCTCACCAAGGAGGCCATGCCGGTGGTCCGCTACCGGACGCGGGACCTGACCCGGCTGCTGCCGG

GCTCGGCACGGGTGTTCCGGCGGATGGAGAAGGTGACCGGGCGCAGTGACGACCTGGTGATCCTGCGCGGGGTGA

ACCTGTTCCCCACCCAGATCGAGGAGATCGTGCTGCG//pOJ260//TTAACCGTCGTACATGCTGACCCTCCTC

GACGAGTTCGAGCGGCAGGGCGTCGACCCGCGCGCGACCTCGCTGAAAGTCGGGATCTTCGGAGCCGAGCCGTGG

ACGGAGGAGATGCGCCGCGAGATCGAGGAGCGCTTCGCCATCGACGCGGTCGACATATACGGGCTGTCGGAGGTG

ATCGGGCCCGGGGTGGCGCAGGAGTGCGTGGAGACCAAGGACGGGCTGCACATCTGGGAGGACCACTTCTACCCG

GAGATCGTCGACCCGCTCACCGGCGAGGTGCTGCCCGAGGGCGAGCGCGGCGAGCTGGTCTTCACCTCGCTCACC

AAGGAGGCCATGCCGGTGGTCCGCTACCGGACGCGGGACCTGACCCGGCTGCTGCCGGGCTCGGCACGGGTGTTC

CGGCGGATGGAGAAGGTGACCGGGCGCAGTGACGACCTGGTGATCCTGCGCGGGGTGAACCTGTTCCCCACCCAG

Appendix C

259

ATCGAGGAGATCGTGCTGC//GCACGCCCGGCCTCGCCCCCCACTTCCAGCTGCGGCTCACCAAGGAGGGCCGCC

TCGAC

> S. polyantibioticus ∆AD2

CCAGCCGACCGGGTGCTGGCTCAATGCCGGACCGAGCTGCCCGTCTACATCATTTATACCTCCGG//CTCCACCG

GCCTGCCGAAGGGTGTGGCAGTTCCGCACAGTTCGTGCGACAACATGGTGGAGTGGCAACGGACGCATTCGGTTC

GGCCCGACCTGAGGACTGCCCAGTACGCGCCGCTGAACTTCGATGTGTGCTTCCAGGAGATTCTCGGCACCCTGT

GCGGCGGCGGCACGCTCGTCGTAGTACCCGAGCGGCTCAGACGCGATCCGATCTCCCTGCTCGACTGGCTCGTGG

TGAACCGTATCGAGCGACTGTTCCTCCCCTGCGTGGCCCTTCATATGCTCACGGTCGCTGCCACCGCCGTGCATT

CACTCGCCGGTCTGGTCCTGGCGGAGATCAATGCCGCCGGTGAGCAGCTGGTCTGCACGCCGGCCATCAGAGATT

TCTTCGCGTTGCTGCCCGGTTGCCGACTGAACAACCACTACGGGCAGAGCGAATCGGCGATGGTCACGGTCCACA

CGCTGACCGGCCCCAGCCGGGAGTGGCCCGCGCTGGCTCCCATCGGCCGGCCACTGCCGGGATGCGAGGTGCTGA

TCGACCCCCCAGACCTCGAAGAGCCGGATGTCGGGGAACTGTTGGTGGCCGGAGCGCCTCTGTCGGCGGGATACC

TCAATCAGCCCCAACTCAGCGCCGAGCGGTATGTCACCGTCGATTCAACTCCGCAGGGACACACTCGTGCCTTCC

GGACGGGTGACCTCG//pOJ260//TTAACTCCACCGGCCTGCCGAAGGGTGTGGCAGTTCCGCACAGTTCGTGC

GACAACATGGTGGAGTGGCAACGGACGCATTCGGTTCGGCCCGACCTGAGGACTGCCCAGTACGCGCCGCTGAAC

TTCGATGTGTGCTTCCAGGAGATTCTCGGCACCCTGTGCGGCGGCGGCACGCTCGTCGTAGTACCCGAGCGGCTC

AGACGCGATCCGATCTCCCTGCTCGACTGGCTCGTGGTGAACCGTATCGAGCGACTGTTCCTCCCCTGCGTGGCC

CTTCATATGCTCACGGTCGCTGCCACCGCCGTGCATTCACTCGCCGGTCTGGTCCTGGCGGAGATCAATGCCGCC

GGTGAGCAGCTGGTCTGCACGCCGGCCATCAGAGATTTCTTCGCGTTGCTGCCCGGTTGCCGACTGAACAACCAC

TACGGGCAGAGCGAATCGGCGATGGTCACGGTCCACACGCTGACCGGCCCCAGCCGGGAGTGGCCCGCGCTGGCT

CCCATCGGCCGGCCACTGCCGGGATGCGAGGTGCTGATCGACCCCCCAGACCTCGAAGAGCCGGATGTCGGGGAA

CTGTTGGTGGCCGGAGCGCCTCTGTCGGCGGGATACCTCAATCAGCCCCAACTCAGCGCCGAGCGGTATGTCACC

GTCGATTCAACTCCGCAGGGACACACTCGTGCCTTCCGGACGGGTGACCTC//GTCCGGGTCGACGGGGACGTGC


CTGCCCGTGGTGCGGGCGGCCGACGCGCCCGAGGCGGCGGTGGACCGCGTCGCGGACGCGCACACC//GCGTACG

TGATGTACACCTCGGGATCGACCGGCCGCCCCAAGGGCGTGGCCGTGACGCACCGCAACATCCTGGCGCTCGCCG

CCGACCCCCTGTGGGCCGACGGCAGCCACACCCGGGTCCTCGCGCACGCGCCGCACTCCTTCGACGCCTCCACCT

TCGAGGTGTGGGTGCCGCTCCTTTGCGGCGGCACGGTCGTGGTGGCCCCGCCGTCCGACTCGGCGGCGCACGCCC

TGGAGCGGACGGTGGCACAGCACCGCCCGACCAGCGCCTTCGTCACCGCGTCCTTGTTCAACTCCCTGGTCGCCG

AGGGCAGTCCCGCCCTCGCCGGGCTGCAACACGTCCTGGTCGGCGGCGAAGCCCCTTCGGCGGCGGCCGTGCGGC

AGTTCCTGGCCGCCTCTCCCGGCACGGCGCTGACCAACGCCTACGGGCCGACCGAGAACACCACCTTCACGACCT

GCCACCGCTACGAGCCGGGCGCCGACGGCAGCCCCACGATCGGCCGGCCGATGGCCAACACCCGGGCCTACGTCC

TGGACGAGCGGCTGCACCCCGTACCCACCGGCGTCGTCGGCGAGCTGTACATCGCGGGCGCGGGCCTGGCCCGCG

GCTACCTCCACAACCCTGGCCTCACCGCCGGGCGGTTCGTCGCCGACCCCTTCGGCGCGCCGGGCGAGCGGATG/

/pOJ260//TTAAGCGTACGTGATGTACACCTCGGGATCGACCGGCCGCCCCAAGGGCGTGGCCGTGACGCACCG

CAACATCCTGGCGCTCGCCGCCGACCCCCTGTGGGCCGACGGCAGCCACACCCGGGTCCTCGCGCACGCGCCGCA

CTCCTTCGACGCCTCCACCTTCGAGGTGTGGGTGCCGCTCCTTTGCGGCGGCACGGTCGTGGTGGCCCCGCCGTC

CGACTCGGCGGCGCACGCCCTGGAGCGGACGGTGGCACAGCACCGCCCGACCAGCGCCTTCGTCACCGCGTCCTT

GTTCAACTCCCTGGTCGCCGAGGGCAGTCCCGCCCTCGCCGGGCTGCAACACGTCCTGGTCGGCGGCGAAGCCCC

TTCGGCGGCGGCCGTGCGGCAGTTCCTGGCCGCCTCTCCCGGCACGGCGCTGACCAACGCCTACGGGCCGACCGA

GAACACCACCTTCACGACCTGCCACCGCTACGAGCCGGGCGCCGACGGCAGCCCCACGATCGGCCGGCCGATGGC

CAACACCCGGGCCTACGTCCTGGACGAGCGGCTGCACCCCGTACCCACCGGCGTCGTCGGCGAGCTGTACATCGC

GGGCGCGGGCCTGGCCCGCGGCTACCTCCACAACCCTGGCCTCACCGCCGGGCGGTTCGTCGCCGACCCCTTCGG

CGCGCCGGGCGAGCGGAT//TACCGCACCGGGGACCTCGCACGGTGGAACGCGGACGGCGACATCGTCTTCACAG


GCCTTACAAGCGCCCCACGACGTGACCGATGGTGAGCGGGCGAGCGGGCTCACCGCCGACCACCCG//GCGTACG

TCATCTACACCTCCGGCTCGACGGGCAAGCCCAAAGGCGTGGTGATGACCCACCGCGGGCTCGCCAGTCTGGCCG

CCGACCACATCGAGCGGTTCGGGATCGTCGAGGGCGACGGGGTGCTCCAGTTCGCCTCGTTCAACTTCGACTGCT

CGGTGGGCGACCTGGTGATGGCGCTGGCCTCGGGCTCGGCGCTCATCGTACGGCCGCAGGACTGTCTGTCCGGGC

ACCAGCTGGGCGAGTTGATCGAGCGGACGTCCGCCACCCATGTGACGATCCCGCCGCAGGTCCTCGCCGCGCTGC

CGCCGGCCGCGCACCCCACCCTGAAGTCGGTCGCCACCGCCGGTGACGTGCTCACCGCCGAGCTCGTGGCCCAAT

GGGCGCCGGGGCGGCGGATGTTCAACGCCTACGGCCCGACCGAGACCACCGTGGACTCGCTGGCCACCGAGGTCG

AGGCCGGTTCGGGTGCCCCGCCGATCGGGCGGCCCCTGGTGAACACCCGGGTGTATGTGCTCGACGACGACATGC

GGCCGCTGCCCGTCGGCGCCGAGGGCGAGCTGTTCATCGCGGGTGCGGGGCTCGCCCGCGGCTATCTGCGTCAAC

CCGGGCTCACCGCCGAGCGGTTCGTGCCCTGCCCGTTCGGGGAGCCGGGCGAGCGCATGG//pOJ260//TTAAG

Appendix C

260

CGTACGTCATCTACACCTCCGGCTCGACGGGCAAGCCCAAAGGCGTGGTGATGACCCACCGCGGGCTCGCCAGTC

TGGCCGCCGACCACATCGAGCGGTTCGGGATCGTCGAGGGCGACGGGGTGCTCCAGTTCGCCTCGTTCAACTTCG

ACTGCTCGGTGGGCGACCTGGTGATGGCGCTGGCCTCGGGCTCGGCGCTCATCGTACGGCCGCAGGACTGTCTGT

CCGGGCACCAGCTGGGCGAGTTGATCGAGCGGACGTCCGCCACCCATGTGACGATCCCGCCGCAGGTCCTCGCCG

CGCTGCCGCCGGCCGCGCACCCCACCCTGAAGTCGGTCGCCACCGCCGGTGACGTGCTCACCGCCGAGCTCGTGG

CCCAATGGGCGCCGGGGCGGCGGATGTTCAACGCCTACGGCCCGACCGAGACCACCGTGGACTCGCTGGCCACCG

AGGTCGAGGCCGGTTCGGGTGCCCCGCCGATCGGGCGGCCCCTGGTGAACACCCGGGTGTATGTGCTCGACGACG

ACATGCGGCCGCTGCCCGTCGGCGCCGAGGGCGAGCTGTTCATCGCGGGTGCGGGGCTCGCCCGCGGCTATCTGC

GTCAACCCGGGCTCACCGCCGAGCGGTTCGTGCCCTGCCCGTTCGGGGAGCCGGGCGAGCGCATG//TACCGCAC


CGGTGCGTACGACAGCGCCGAACCGGCCGCCGTCGCCGTCGACATCGACGACTGGGCGTACGGCGG//ACCTCGG

GTTCCACGGGCAAGCCCAAGGGCGTCGTGACCGAGTACGCCGGACTCACCAACATGCTGATCAACCACCAGCGCC

GGATCTTCGAGCCGGTGCTGGCGGAGCACGGCGACCGGGTGTTCCGGATCGCCCACACCGTGTCGTTCGCGTTCG

ACATGTCGTGGGAGGAGCTGCTGTGGCTCGCCGACGGCCACGAGGTGCACATCTGCGACGAGGAACTGCGCCGCG

ACGCGCCCGCCCTGGTCGAGTACTGCGGCGAGCACGGGATCGACGTCATCAACGTGGCCCCCACGTACACGCAGC

AGCTGGTGGCCGAGGGCCTGCTCGACAACCCGGCCCGGCGCCCCGCGCTGGTGCTGCTGGGCGGCGAGGCGGTCA

CCCCGACCCTGTGGCAGCGGCTCGCCGGCACCGAGGGAACGGTCGGCTACAACCTGTACGGACCCACCGAGTACA

CCATCAACACCCTGGGCGTCGGCACCTTCGAGTGCGAGGACCCGGTGGTGGGCGTGGCGATCGACAACACCGACG

TGTTCGTGCTGGACCCGTGGCTGCGGCCGCTCCCGGACGGAGTTCCGGGTGAGCTCCACGTCACGGGCGTCGGCA

TCGCCCGCGGCTATCTGGGCTAGCACGCCCAGACCGCGCACCGGTTCGTGGCGTCCCCGTTCGGCGAGCCCGGCG

AGCGCATGTACCGCACCGGTGACCTCG//POJ260//TTAAACCTCGGGTTCCACGGGCAAGCCCAAGGGCGTCG

TGACCGAGTACGCCGGACTCACCAACATGCTGATCAACCACCAGCGCCGGATCTTCGAGCCGGTGCTGGCGGAGC

ACGGCGACCGGGTGTTCCGGATCGCCCACACCGTGTCGTTCGCGTTCGACATGTCGTGGGAGGAGCTGCTGTGGC

TCGCCGACGGCCACGAGGTGCACATCTGCGACGAGGAACTGCGCCGCGACGCGCCCGCCCTGGTCGAGTACTGCG

GCGAGCACGGGATCGACGTCATCAACGTGGCCCCCACGTACACGCAGCAGCTGGTGGCCGAGGGCCTGCTCGACA

ACCCGGCCCGGCGCCCCGCGCTGGTGCTGCTGGGCGGCGAGGCGGTCACCCCGACCCTGTGGCAGCGGCTCGCCG

GCACCGAGGGAACGGTCGGCTACAACCTGTACGGACCCACCGAGTACACCATCAACACCCTGGGCGTCGGCACCT

TCGAGTGCGAGGACCCGGTGGTGGGCGTGGCGATCGACAACACCGACGTGTTCGTGCTGGACCCGTGGCTGCGGC

CGCTCCCGGACGGAGTTCCGGGTGAGCTCCACGTCACGGGCGTCGGCATCGCCCGCGGCTATCTGGGCTAGCACG

CCCAGACCGCGCACCGGTTCGTGGCGTCCCCGTTCGGCGAGCCCGGCGAGCGCATGTACCGCACCGGTGACCTC

//ACGAGCTGCG


GCGCCGCCACCGCGCGCAGCCTGGCGTACGTCATCTACACCTCCGGCTCCACCGGCCGCCCCAAGG//GCCTACG

TGATCTACACCTCGGGGTCCACCGGCACGCCCAAGGGCGTGATGGTCGAACACCGCAATGCCACCCGGCTGTTCA

CCGCCACCGAGCCGTGGTTCGGCTTCGGCCGCGACGACGTGTGGACGCTGTTCCACTCCTTCGCCTTCGACTTCT

CCGTGTGGGAGATCTGGGGCGCGCTGCTGCACGGCGGCCGTCTGGTGATCGTGCCGCAGGCCACCACCCGCAACC

CGAACGACTTCTACGCCCTGCTGTGCGCGGAGGGGGTGACCGTCCTCAACCAGACGCCCAGCGCCTTCCGGCAGC

TGATCGCGGCCCAGGGCGACAGCCCGGCCGCACACCGGCTGCGCACGGTCGTCTTCGGCGGCGAGGCCCTGGACG

TCGCCGCACTCAAGCCGTGGCTGCGCCGCGCGGCCAACAAGGGCACCCGGCTCGTCAACATGTACGGGATCACCG

AGACCACCGTGCATGTCACCTACCGGCCGCTGACCGAGGCCGACGCGGAGCTCGCGGTGAGCCCGATCGGCGAAC

GGATCCCCGACCTGCGCACCTACGTCCTGGACCGGCACGGGCGGCCCGCCCCCGTCGGCGCGGTCGGCGAGCTGT

ATGTCGGCGGTGACGGCGTGGCCCGCGGCTACCTCAACCGGCCCGAGCTCACCGCCGAGCGCTTCCTGGACGACC

CGTTCTGCCCCGAGCCCGATGAGCGGATGTACCGCACCGGCGACGTCG//POJ260//TTAAGCCTACGTGATCT

ACACCTCGGGGTCCACCGGCACGCCCAAGGGCGTGATGGTCGAACACCGCAATGCCACCCGGCTGTTCACCGCCA

CCGAGCCGTGGTTCGGCTTCGGCCGCGACGACGTGTGGACGCTGTTCCACTCCTTCGCCTTCGACTTCTCCGTGT

GGGAGATCTGGGGCGCGCTGCTGCACGGCGGCCGTCTGGTGATCGTGCCGCAGGCCACCACCCGCAACCCGAACG

ACTTCTACGCCCTGCTGTGCGCGGAGGGGGTGACCGTCCTCAACCAGACGCCCAGCGCCTTCCGGCAGCTGATCG

CGGCCCAGGGCGACAGCCCGGCCGCACACCGGCTGCGCACGGTCGTCTTCGGCGGCGAGGCCCTGGACGTCGCCG

CACTCAAGCCGTGGCTGCGCCGCGCGGCCAACAAGGGCACCCGGCTCGTCAACATGTACGGGATCACCGAGACCA

CCGTGCATGTCACCTACCGGCCGCTGACCGAGGCCGACGCGGAGCTCGCGGTGAGCCCGATCGGCGAACGGATCC

CCGACCTGCGCACCTACGTCCTGGACCGGCACGGGCGGCCCGCCCCCGTCGGCGCGGTCGGCGAGCTGTATGTCG

GCGGTGACGGCGTGGCCCGCGGCTACCTCAACCGGCCCGAGCTCACCGCCGAGCGCTTCCTGGACGACCCGTTCT

GCCCCGAGCCCGATGAGCGGATGTACCGCACCGGCGACGTC//GTACGGCGCCTCGCGGACGGCACCCTGGAATT

Date post:	20-Feb-2023
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diphenyloxazole biosynthetic pathway in streptomyces ...

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